diff --git a/aoc/aoc.c b/aoc/aoc.c
index 2161e64..dd2acb4 100644
--- a/aoc/aoc.c
+++ b/aoc/aoc.c
@@ -28,7 +28,7 @@ Tokens str_tokenize(Arena *arena, str s, str delim) {
 
     str stuff = s;
     isize token_count = 0;
-    while (str_next_token(&stuff, delim).len > 0) {
+    for (; stuff.len > 0; str_next_token(&stuff, delim)) {
         token_count++;
     }
 
diff --git a/aoc/common.h b/aoc/common.h
index 552bf6f..1e4becd 100644
--- a/aoc/common.h
+++ b/aoc/common.h
@@ -98,76 +98,3 @@ typedef double f64;
 #define MAX(a, b) ((a) > (b) ? (a) : (b))
 #define MIN(a, b) ((a) < (b) ? (a) : (b))
 #define CLAMP(x, lo, hi) ((x) < (lo) ? (lo) : (x) > (hi) ? (hi) : (x))
-
-typedef union Vec2 {
-    struct { f32 x, y; };
-    struct { f32 u, v; };
-} Vec2;
-
-typedef union Vec2i {
-    struct { i32 x, y; };
-    struct { i32 u, v; };
-} Vec2i ;
-
-typedef struct Mat4 {
-    float e[4][4];
-} Mat4;
-
-
-static inline Vec2
-vec2_add(Vec2 a, Vec2 b) {
-    Vec2 result = {
-        .x = a.x + b.x,
-        .y = a.y + b.y,
-    };
-    return result;
-}
-
-static inline Vec2
-vec2_sub(Vec2 a, Vec2 b) {
-    Vec2 result = {
-        .x = a.x - b.x,
-        .y = a.y - b.y,
-    };
-    return result;
-}
-
-static inline Vec2
-vec2(f32 x, f32 y) {
-    Vec2 result = {{ x, y }};
-    return result;
-}
-
-static inline f32
-vec2_dot(Vec2 a, Vec2 b) {
-    return a.x * b.x + a.y * b.y;
-}
-
-static inline f32
-vec2_norm2(Vec2 v) {
-    return vec2_dot(v, v);
-}
-
-static inline f32
-vec2_norm(Vec2 v) {
-    return sqrtf(vec2_norm2(v));
-}
-
-static inline f32
-vec2_dist(Vec2 a, Vec2 b) {
-    return vec2_norm(vec2_sub(a, b));
-}
-
-typedef struct Rect2i {
-    int x, y, w, h;
-} Rect2i;
-
-typedef struct Rect2f {
-    f32 x, y, w, h;
-} Rect2f;
-
-static inline Rect2f
-rect2f(f32 x, f32 y, f32 w, f32 h) {
-    Rect2f result = { x, y, w, h };
-    return result;
-}
diff --git a/day-13/input.txt b/day-13/input.txt
new file mode 100644
index 0000000..201bbd5
--- /dev/null
+++ b/day-13/input.txt
@@ -0,0 +1,1279 @@
+Button A: X+92, Y+17
+Button B: X+27, Y+61
+Prize: X=9152, Y=6172
+
+Button A: X+12, Y+61
+Button B: X+41, Y+12
+Prize: X=8771, Y=12729
+
+Button A: X+71, Y+11
+Button B: X+14, Y+54
+Prize: X=7189, Y=5889
+
+Button A: X+22, Y+36
+Button B: X+49, Y+21
+Prize: X=8122, Y=6806
+
+Button A: X+44, Y+88
+Button B: X+72, Y+36
+Prize: X=4972, Y=4004
+
+Button A: X+11, Y+57
+Button B: X+50, Y+18
+Prize: X=3024, Y=17456
+
+Button A: X+88, Y+91
+Button B: X+80, Y+13
+Prize: X=12096, Y=8255
+
+Button A: X+22, Y+50
+Button B: X+48, Y+28
+Prize: X=17238, Y=1530
+
+Button A: X+67, Y+19
+Button B: X+25, Y+70
+Prize: X=15607, Y=12559
+
+Button A: X+20, Y+58
+Button B: X+67, Y+22
+Prize: X=13571, Y=12102
+
+Button A: X+36, Y+74
+Button B: X+82, Y+39
+Prize: X=6484, Y=8146
+
+Button A: X+15, Y+73
+Button B: X+89, Y+17
+Prize: X=9054, Y=4114
+
+Button A: X+40, Y+23
+Button B: X+12, Y+41
+Prize: X=10476, Y=1521
+
+Button A: X+61, Y+30
+Button B: X+43, Y+71
+Prize: X=5659, Y=5525
+
+Button A: X+56, Y+20
+Button B: X+36, Y+75
+Prize: X=15692, Y=11255
+
+Button A: X+12, Y+54
+Button B: X+28, Y+27
+Prize: X=540, Y=945
+
+Button A: X+62, Y+18
+Button B: X+47, Y+71
+Prize: X=8201, Y=6109
+
+Button A: X+55, Y+90
+Button B: X+95, Y+35
+Prize: X=7345, Y=9610
+
+Button A: X+92, Y+77
+Button B: X+26, Y+76
+Prize: X=9400, Y=9820
+
+Button A: X+76, Y+75
+Button B: X+12, Y+66
+Prize: X=2440, Y=5874
+
+Button A: X+82, Y+12
+Button B: X+56, Y+95
+Prize: X=2336, Y=2946
+
+Button A: X+63, Y+82
+Button B: X+72, Y+14
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+
+Button A: X+35, Y+72
+Button B: X+57, Y+14
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+
+Button A: X+80, Y+24
+Button B: X+33, Y+89
+Prize: X=8581, Y=5501
+
+Button A: X+68, Y+37
+Button B: X+42, Y+88
+Prize: X=7270, Y=5845
+
+Button A: X+12, Y+52
+Button B: X+34, Y+12
+Prize: X=7922, Y=17576
+
+Button A: X+61, Y+74
+Button B: X+76, Y+23
+Prize: X=7511, Y=2884
+
+Button A: X+84, Y+33
+Button B: X+12, Y+18
+Prize: X=3372, Y=2268
+
+Button A: X+32, Y+68
+Button B: X+52, Y+19
+Prize: X=3288, Y=3522
+
+Button A: X+18, Y+57
+Button B: X+71, Y+15
+Prize: X=3948, Y=6983
+
+Button A: X+80, Y+40
+Button B: X+23, Y+67
+Prize: X=5874, Y=7266
+
+Button A: X+81, Y+53
+Button B: X+19, Y+79
+Prize: X=3362, Y=4330
+
+Button A: X+37, Y+79
+Button B: X+95, Y+26
+Prize: X=4045, Y=3862
+
+Button A: X+89, Y+36
+Button B: X+58, Y+91
+Prize: X=7323, Y=6204
+
+Button A: X+28, Y+23
+Button B: X+11, Y+91
+Prize: X=1531, Y=7241
+
+Button A: X+28, Y+60
+Button B: X+62, Y+20
+Prize: X=16504, Y=6340
+
+Button A: X+23, Y+71
+Button B: X+94, Y+75
+Prize: X=1711, Y=1839
+
+Button A: X+18, Y+54
+Button B: X+60, Y+13
+Prize: X=6068, Y=16687
+
+Button A: X+11, Y+44
+Button B: X+69, Y+23
+Prize: X=770, Y=1009
+
+Button A: X+83, Y+60
+Button B: X+13, Y+45
+Prize: X=3334, Y=3585
+
+Button A: X+30, Y+60
+Button B: X+50, Y+13
+Prize: X=19290, Y=15493
+
+Button A: X+26, Y+79
+Button B: X+94, Y+35
+Prize: X=7188, Y=7806
+
+Button A: X+29, Y+60
+Button B: X+53, Y+13
+Prize: X=11472, Y=418
+
+Button A: X+97, Y+86
+Button B: X+13, Y+99
+Prize: X=2527, Y=8801
+
+Button A: X+67, Y+99
+Button B: X+98, Y+27
+Prize: X=3521, Y=3789
+
+Button A: X+55, Y+77
+Button B: X+37, Y+15
+Prize: X=14225, Y=12883
+
+Button A: X+13, Y+20
+Button B: X+41, Y+18
+Prize: X=1233, Y=770
+
+Button A: X+97, Y+48
+Button B: X+14, Y+57
+Prize: X=8380, Y=7752
+
+Button A: X+12, Y+61
+Button B: X+69, Y+17
+Prize: X=3305, Y=1545
+
+Button A: X+15, Y+56
+Button B: X+64, Y+31
+Prize: X=3453, Y=3344
+
+Button A: X+45, Y+62
+Button B: X+33, Y+12
+Prize: X=3635, Y=16852
+
+Button A: X+36, Y+12
+Button B: X+12, Y+33
+Prize: X=10856, Y=4394
+
+Button A: X+55, Y+89
+Button B: X+82, Y+24
+Prize: X=3886, Y=2158
+
+Button A: X+26, Y+73
+Button B: X+97, Y+68
+Prize: X=9733, Y=7097
+
+Button A: X+87, Y+46
+Button B: X+11, Y+52
+Prize: X=1369, Y=15432
+
+Button A: X+48, Y+20
+Button B: X+37, Y+68
+Prize: X=12376, Y=4116
+
+Button A: X+34, Y+75
+Button B: X+77, Y+31
+Prize: X=3397, Y=5966
+
+Button A: X+26, Y+59
+Button B: X+35, Y+18
+Prize: X=12833, Y=3002
+
+Button A: X+16, Y+65
+Button B: X+92, Y+19
+Prize: X=4248, Y=3777
+
+Button A: X+65, Y+21
+Button B: X+29, Y+68
+Prize: X=3813, Y=14170
+
+Button A: X+37, Y+12
+Button B: X+28, Y+43
+Prize: X=3647, Y=5762
+
+Button A: X+66, Y+28
+Button B: X+31, Y+84
+Prize: X=2952, Y=4228
+
+Button A: X+48, Y+86
+Button B: X+73, Y+31
+Prize: X=7120, Y=6370
+
+Button A: X+81, Y+34
+Button B: X+50, Y+93
+Prize: X=8280, Y=6068
+
+Button A: X+26, Y+50
+Button B: X+87, Y+32
+Prize: X=4167, Y=1654
+
+Button A: X+19, Y+98
+Button B: X+33, Y+19
+Prize: X=3742, Y=4331
+
+Button A: X+17, Y+52
+Button B: X+61, Y+22
+Prize: X=3176, Y=9284
+
+Button A: X+18, Y+41
+Button B: X+71, Y+43
+Prize: X=8552, Y=2649
+
+Button A: X+51, Y+14
+Button B: X+66, Y+89
+Prize: X=6510, Y=8450
+
+Button A: X+11, Y+38
+Button B: X+58, Y+13
+Prize: X=13236, Y=9231
+
+Button A: X+26, Y+15
+Button B: X+32, Y+56
+Prize: X=13378, Y=1307
+
+Button A: X+48, Y+12
+Button B: X+43, Y+77
+Prize: X=8151, Y=4369
+
+Button A: X+83, Y+28
+Button B: X+19, Y+24
+Prize: X=6854, Y=2664
+
+Button A: X+45, Y+53
+Button B: X+56, Y+17
+Prize: X=8035, Y=5547
+
+Button A: X+57, Y+26
+Button B: X+13, Y+24
+Prize: X=5477, Y=3456
+
+Button A: X+64, Y+34
+Button B: X+20, Y+48
+Prize: X=14540, Y=13044
+
+Button A: X+63, Y+39
+Button B: X+41, Y+78
+Prize: X=5827, Y=6396
+
+Button A: X+75, Y+15
+Button B: X+15, Y+71
+Prize: X=18125, Y=11885
+
+Button A: X+67, Y+25
+Button B: X+57, Y+82
+Prize: X=4467, Y=3428
+
+Button A: X+67, Y+19
+Button B: X+18, Y+47
+Prize: X=11739, Y=7909
+
+Button A: X+11, Y+66
+Button B: X+76, Y+13
+Prize: X=18011, Y=14042
+
+Button A: X+71, Y+82
+Button B: X+78, Y+18
+Prize: X=6875, Y=4408
+
+Button A: X+39, Y+52
+Button B: X+53, Y+14
+Prize: X=4891, Y=2668
+
+Button A: X+44, Y+25
+Button B: X+14, Y+44
+Prize: X=17914, Y=12221
+
+Button A: X+82, Y+38
+Button B: X+46, Y+94
+Prize: X=8364, Y=6856
+
+Button A: X+18, Y+59
+Button B: X+64, Y+27
+Prize: X=16262, Y=18991
+
+Button A: X+55, Y+70
+Button B: X+91, Y+11
+Prize: X=7510, Y=2745
+
+Button A: X+31, Y+13
+Button B: X+11, Y+92
+Prize: X=943, Y=6163
+
+Button A: X+42, Y+70
+Button B: X+67, Y+26
+Prize: X=6861, Y=7066
+
+Button A: X+49, Y+20
+Button B: X+14, Y+39
+Prize: X=2065, Y=4005
+
+Button A: X+69, Y+11
+Button B: X+54, Y+56
+Prize: X=5592, Y=1318
+
+Button A: X+69, Y+35
+Button B: X+12, Y+44
+Prize: X=4697, Y=2487
+
+Button A: X+85, Y+19
+Button B: X+41, Y+51
+Prize: X=2901, Y=1527
+
+Button A: X+52, Y+14
+Button B: X+23, Y+67
+Prize: X=16545, Y=3463
+
+Button A: X+43, Y+14
+Button B: X+13, Y+61
+Prize: X=19114, Y=16830
+
+Button A: X+42, Y+71
+Button B: X+93, Y+21
+Prize: X=4809, Y=3362
+
+Button A: X+79, Y+34
+Button B: X+45, Y+99
+Prize: X=8849, Y=9542
+
+Button A: X+62, Y+22
+Button B: X+38, Y+57
+Prize: X=6450, Y=5770
+
+Button A: X+31, Y+67
+Button B: X+83, Y+56
+Prize: X=5663, Y=8291
+
+Button A: X+15, Y+50
+Button B: X+38, Y+19
+Prize: X=3628, Y=7019
+
+Button A: X+83, Y+31
+Button B: X+46, Y+56
+Prize: X=470, Y=292
+
+Button A: X+19, Y+95
+Button B: X+67, Y+15
+Prize: X=6784, Y=8960
+
+Button A: X+20, Y+83
+Button B: X+29, Y+15
+Prize: X=1607, Y=2139
+
+Button A: X+28, Y+52
+Button B: X+91, Y+22
+Prize: X=1141, Y=502
+
+Button A: X+75, Y+27
+Button B: X+45, Y+72
+Prize: X=6960, Y=3231
+
+Button A: X+56, Y+76
+Button B: X+93, Y+13
+Prize: X=12274, Y=7374
+
+Button A: X+86, Y+34
+Button B: X+50, Y+65
+Prize: X=8286, Y=6804
+
+Button A: X+65, Y+24
+Button B: X+14, Y+33
+Prize: X=14442, Y=3530
+
+Button A: X+98, Y+33
+Button B: X+68, Y+78
+Prize: X=9486, Y=4131
+
+Button A: X+37, Y+87
+Button B: X+97, Y+39
+Prize: X=5839, Y=3141
+
+Button A: X+77, Y+32
+Button B: X+30, Y+61
+Prize: X=3936, Y=2024
+
+Button A: X+36, Y+18
+Button B: X+11, Y+35
+Prize: X=8099, Y=8099
+
+Button A: X+96, Y+43
+Button B: X+41, Y+83
+Prize: X=5305, Y=3475
+
+Button A: X+79, Y+11
+Button B: X+32, Y+35
+Prize: X=2181, Y=1556
+
+Button A: X+26, Y+60
+Button B: X+64, Y+23
+Prize: X=3188, Y=11974
+
+Button A: X+42, Y+16
+Button B: X+18, Y+61
+Prize: X=14534, Y=8311
+
+Button A: X+12, Y+48
+Button B: X+79, Y+29
+Prize: X=11975, Y=9941
+
+Button A: X+17, Y+54
+Button B: X+63, Y+30
+Prize: X=2089, Y=10202
+
+Button A: X+62, Y+24
+Button B: X+11, Y+35
+Prize: X=4439, Y=13677
+
+Button A: X+46, Y+57
+Button B: X+55, Y+15
+Prize: X=5256, Y=4812
+
+Button A: X+34, Y+17
+Button B: X+25, Y+56
+Prize: X=10318, Y=7437
+
+Button A: X+19, Y+82
+Button B: X+67, Y+47
+Prize: X=1736, Y=4102
+
+Button A: X+46, Y+19
+Button B: X+35, Y+66
+Prize: X=11211, Y=10607
+
+Button A: X+47, Y+64
+Button B: X+93, Y+40
+Prize: X=11287, Y=7832
+
+Button A: X+70, Y+40
+Button B: X+14, Y+81
+Prize: X=3332, Y=6868
+
+Button A: X+81, Y+11
+Button B: X+11, Y+72
+Prize: X=4578, Y=8951
+
+Button A: X+24, Y+52
+Button B: X+57, Y+15
+Prize: X=18755, Y=16053
+
+Button A: X+95, Y+41
+Button B: X+32, Y+83
+Prize: X=7637, Y=4403
+
+Button A: X+25, Y+52
+Button B: X+59, Y+21
+Prize: X=4618, Y=15514
+
+Button A: X+62, Y+24
+Button B: X+30, Y+68
+Prize: X=5346, Y=1736
+
+Button A: X+14, Y+37
+Button B: X+66, Y+37
+Prize: X=17488, Y=17306
+
+Button A: X+68, Y+24
+Button B: X+69, Y+95
+Prize: X=5094, Y=6178
+
+Button A: X+19, Y+29
+Button B: X+99, Y+19
+Prize: X=1926, Y=826
+
+Button A: X+15, Y+33
+Button B: X+63, Y+23
+Prize: X=13331, Y=11029
+
+Button A: X+90, Y+12
+Button B: X+12, Y+65
+Prize: X=6102, Y=5949
+
+Button A: X+31, Y+68
+Button B: X+56, Y+12
+Prize: X=16228, Y=8080
+
+Button A: X+28, Y+73
+Button B: X+57, Y+17
+Prize: X=14247, Y=3172
+
+Button A: X+11, Y+26
+Button B: X+37, Y+23
+Prize: X=13427, Y=7273
+
+Button A: X+41, Y+19
+Button B: X+15, Y+73
+Prize: X=3548, Y=4088
+
+Button A: X+86, Y+82
+Button B: X+24, Y+86
+Prize: X=7332, Y=11346
+
+Button A: X+89, Y+24
+Button B: X+39, Y+78
+Prize: X=6928, Y=4770
+
+Button A: X+31, Y+45
+Button B: X+40, Y+14
+Prize: X=15091, Y=14401
+
+Button A: X+48, Y+26
+Button B: X+16, Y+51
+Prize: X=10016, Y=4137
+
+Button A: X+16, Y+45
+Button B: X+58, Y+20
+Prize: X=14050, Y=5760
+
+Button A: X+15, Y+38
+Button B: X+83, Y+26
+Prize: X=8740, Y=4636
+
+Button A: X+31, Y+52
+Button B: X+36, Y+18
+Prize: X=10505, Y=1352
+
+Button A: X+11, Y+29
+Button B: X+56, Y+31
+Prize: X=3071, Y=15583
+
+Button A: X+41, Y+13
+Button B: X+51, Y+84
+Prize: X=18140, Y=4034
+
+Button A: X+31, Y+20
+Button B: X+11, Y+43
+Prize: X=393, Y=828
+
+Button A: X+54, Y+33
+Button B: X+20, Y+38
+Prize: X=7204, Y=6838
+
+Button A: X+43, Y+65
+Button B: X+41, Y+12
+Prize: X=12942, Y=5307
+
+Button A: X+45, Y+19
+Button B: X+34, Y+69
+Prize: X=16741, Y=19477
+
+Button A: X+35, Y+99
+Button B: X+95, Y+13
+Prize: X=4455, Y=5697
+
+Button A: X+83, Y+88
+Button B: X+68, Y+13
+Prize: X=8324, Y=7939
+
+Button A: X+60, Y+30
+Button B: X+28, Y+47
+Prize: X=4808, Y=3262
+
+Button A: X+65, Y+24
+Button B: X+23, Y+33
+Prize: X=4552, Y=2514
+
+Button A: X+70, Y+11
+Button B: X+96, Y+93
+Prize: X=9974, Y=7333
+
+Button A: X+69, Y+11
+Button B: X+40, Y+95
+Prize: X=4751, Y=2264
+
+Button A: X+12, Y+38
+Button B: X+41, Y+22
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+
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+Button A: X+22, Y+70
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+Button A: X+15, Y+60
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+Button A: X+43, Y+56
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+Button A: X+61, Y+24
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+
+Button A: X+18, Y+97
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+
+Button A: X+72, Y+43
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+
+Button A: X+11, Y+26
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+
+Button A: X+54, Y+23
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+
+Button A: X+57, Y+12
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+
+Button A: X+26, Y+57
+Button B: X+69, Y+34
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+
+Button A: X+14, Y+46
+Button B: X+65, Y+15
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+
+Button A: X+60, Y+34
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+
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+
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+
+Button A: X+26, Y+19
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+
+Button A: X+35, Y+95
+Button B: X+85, Y+28
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+
+Button A: X+80, Y+21
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+
+Button A: X+63, Y+35
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+
+Button A: X+33, Y+59
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+
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+
+Button A: X+48, Y+66
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+
+Button A: X+41, Y+11
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+
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+
+Button A: X+49, Y+24
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+
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+
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+Button B: X+83, Y+17
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+
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+Button B: X+26, Y+26
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
+Button A: X+61, Y+25
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
+Button A: X+69, Y+35
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+
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+
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+
+Button A: X+15, Y+60
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+
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+
+Button A: X+41, Y+27
+Button B: X+13, Y+31
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+
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+
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+Button B: X+27, Y+18
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+
+Button A: X+51, Y+17
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+
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+
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+
+Button A: X+51, Y+21
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+
+Button A: X+70, Y+33
+Button B: X+16, Y+64
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+
+Button A: X+17, Y+43
+Button B: X+84, Y+14
+Prize: X=1396, Y=554
+
+Button A: X+76, Y+35
+Button B: X+22, Y+88
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+
+Button A: X+54, Y+13
+Button B: X+14, Y+62
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+
+Button A: X+55, Y+29
+Button B: X+24, Y+40
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+
+Button A: X+55, Y+49
+Button B: X+11, Y+52
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+
+Button A: X+27, Y+13
+Button B: X+26, Y+42
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+
+Button A: X+60, Y+16
+Button B: X+32, Y+75
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+
+Button A: X+36, Y+69
+Button B: X+64, Y+39
+Prize: X=4668, Y=4680
+
+Button A: X+38, Y+12
+Button B: X+28, Y+56
+Prize: X=2180, Y=1160
+
+Button A: X+31, Y+21
+Button B: X+30, Y+65
+Prize: X=4857, Y=6507
+
+Button A: X+38, Y+56
+Button B: X+38, Y+15
+Prize: X=13686, Y=14581
+
+Button A: X+25, Y+57
+Button B: X+40, Y+17
+Prize: X=11305, Y=8893
+
+Button A: X+13, Y+45
+Button B: X+52, Y+46
+Prize: X=5395, Y=5811
diff --git a/day-13/main.c b/day-13/main.c
new file mode 100644
index 0000000..59514ff
--- /dev/null
+++ b/day-13/main.c
@@ -0,0 +1,94 @@
+#include "aoc.h"
+#include <limits.h>
+#include <ctype.h>
+
+typedef struct Vec2i {
+    i64 x;
+    i64 y;
+} Vec2i;
+
+static Vec2i
+parse_numbers(str line, Arena *arena) {
+    bool x_set = false;
+    Vec2i result = {0};
+    for (isize i = 0; i < line.len; i++) {
+        if (isdigit(line.data[i])) {
+            isize end = i + 1;
+            while (end < line.len && isdigit(line.data[end])) {
+                end++;
+            }
+            str num_str = str_sub(line, i, end);
+            if (!x_set) {
+                result.x = (i32) parse_i64(num_str, *arena);
+                x_set = true;
+            }
+            else {
+                result.y = (i32) parse_i64(num_str, *arena);
+                return result;
+            }
+            i = end;
+        }
+    }
+    NOT_REACHABLE();
+}
+
+static bool 
+solve(Vec2i a, Vec2i b, Vec2i p, Vec2i *solution) {
+    i64 det = a.x * b.y - a.y * b.x;
+    ASSERT(det != 0);
+
+    i64 numerator_a = p.x * b.y - p.y * b.x;
+    i64 numerator_b = p.y * a.x - p.x * a.y;
+    bool solved = false;
+    if ((numerator_a % det == 0) && (numerator_b % det == 0)) {
+        i64 n_a = numerator_a / det;
+        i64 n_b = numerator_b / det;
+        if (n_a >= 0 && n_b >= 0) {
+            solution->x = n_a;
+            solution->y = n_b;
+            solved = true;
+        }
+    }
+    else {
+        // no integer solution
+    }
+    return solved;
+}
+
+int main(int argc, char **argv) {
+    Arena *arena = make_arena(Megabytes(1));
+    str input = read_file(arena, argv[1]);
+
+    str line;
+    i64 part_1 = 0;
+    i64 part_2 = 0;
+    while (input.len > 0) {
+        str a_line = str_next_token(&input, STR("\n"));
+        str b_line = str_next_token(&input, STR("\n"));
+        str prize_line = str_next_token(&input, STR("\n"));
+        str empty_line = str_next_token(&input, STR("\n"));
+        ASSERT(str_trim(empty_line).len == 0);
+
+        Vec2i a = parse_numbers(a_line, arena);
+        Vec2i b = parse_numbers(b_line, arena);
+        Vec2i p = parse_numbers(prize_line, arena);
+        Vec2i p_ = { p.x + 10000000000000ull, p.y + 10000000000000ull };
+
+#if 0
+        printf("a: %ld %ld\n", a.x, a.y);
+        printf("b: %ld %ld\n", b.x, b.y);
+        printf("p: %ld %ld\n", p.x, p.y);
+        printf("\n");
+#endif
+        Vec2i n;
+        if (solve(a, b, p, &n)) {
+            part_1 += n.x * 3 + n.y;
+        }
+
+        if (solve(a, b, p_, &n)) {
+            part_2 += n.x * 3 + n.y;
+        }
+    }
+    printf("%ld\n", part_1);
+    printf("%ld\n", part_2);
+}
diff --git a/day-13/test.txt b/day-13/test.txt
new file mode 100644
index 0000000..444a287
--- /dev/null
+++ b/day-13/test.txt
@@ -0,0 +1,15 @@
+Button A: X+94, Y+34
+Button B: X+22, Y+67
+Prize: X=8400, Y=5400
+
+Button A: X+26, Y+66
+Button B: X+67, Y+21
+Prize: X=12748, Y=12176
+
+Button A: X+17, Y+86
+Button B: X+84, Y+37
+Prize: X=7870, Y=6450
+
+Button A: X+69, Y+23
+Button B: X+27, Y+71
+Prize: X=18641, Y=10279
\ No newline at end of file