diff --git a/13/13.py b/13/13.py
new file mode 100755
index 0000000..a39a872
--- /dev/null
+++ b/13/13.py
@@ -0,0 +1,114 @@
+#!/usr/bin/env python
+# 2021 - Advent Of Code - 13
+
+
+def parse_file(file):
+    parsed_dots = []
+    parsed_folds = []
+    with open(file) as f:
+        for line in f.readlines():
+            if line.startswith('fold along '):
+                _, f = line.strip().split('fold along ')
+                parsed_folds.append(f.split('='))
+            elif line == '\n':
+                pass
+            else:
+                dot = [int(d) for d in line.strip().split(',')]
+                parsed_dots.append(dot)
+        return parsed_dots, parsed_folds
+
+
+def find_max(dot_list):
+    mx = 0
+    my = 0
+    for d in dot_list:
+        if d[0] > mx:
+            mx = d[0]
+        if d[1] > my:
+            my = d[1]
+
+    return mx, my
+
+
+def place_dots(g, dots_list):
+    for dot in dots_list:
+        g[dot[1]][dot[0]] = 1
+
+
+def print_grid(g, fold=-1):
+    for y, _ in enumerate(g):
+        if y == fold:
+            for x, _ in enumerate(g[y]):
+                print('-', end='')
+        else:
+            for x, _ in enumerate(g[y]):
+                if g[y][x] == 1:
+                    print('#', end='')
+                else:
+                    print('.', end='')
+        print()
+
+
+def fold_horizontally(g, fold_y):
+    print(f'folding y={fold_y}')
+    for y in range(fold_y, maxy+1):
+        folding_dist = y - fold_y
+        new_y = fold_y - folding_dist
+
+        # place new dots
+        for x, _ in enumerate(g[y]):
+            if g[y][x] == 1:
+                g[new_y][x] = 1
+
+    # cut the other half of the grid
+    for i in range(fold_y+1):
+        g.pop()
+
+
+def fold_vertically(g, fold_x):
+    print(f'folding x={fold_x}')
+    for y, _ in enumerate(g):
+        # place new dots
+        for x in range(fold_x, maxx+1):
+            folding_dist = x - fold_x
+            new_x = fold_x - folding_dist
+            if g[y][x] == 1:
+                g[y][new_x] = 1
+
+        # cut the other half of the grid
+        g[y] = g[y][:fold_x]
+
+
+def count_dots(g):
+    count = 0
+    for y, _ in enumerate(g):
+        for x, _ in enumerate(g[y]):
+            if g[y][x] == 1:
+                count += 1
+
+    return count
+
+
+# dots, folds = parse_file('input_example.txt')
+dots, folds = parse_file('input.txt')
+
+maxx, maxy = find_max(dots)
+grid = [[0] * (maxx+1) for _ in range(maxy+1)]
+
+# for f in folds:
+#     print(f'folding {f[0]} = {f[1]}')
+# for d in dots:
+#     print(f'dot: {d}')
+
+place_dots(grid, dots)
+# print_grid(grid, 7)
+print(f'grid size: {maxx}, {maxy}')
+
+# folding_y = int(folds[0][1])
+# print()
+# fold_horizontally(grid, folding_y)
+# print()
+fold_vertically(grid, 655)
+
+# print_grid(grid)
+print(f'number of dots: {count_dots(grid)}')
diff --git a/13/input.txt b/13/input.txt
new file mode 100644
index 0000000..8908b2d
--- /dev/null
+++ b/13/input.txt
@@ -0,0 +1,896 @@
+94,530
+698,875
+221,18
+1232,443
+689,509
+1153,225
+239,16
+1265,275
+589,264
+594,766
+882,159
+1245,435
+6,686
+383,488
+497,535
+601,353
+326,330
+1277,509
+773,239
+331,567
+174,43
+1047,551
+771,358
+716,871
+1215,346
+228,357
+703,647
+1272,299
+363,668
+967,248
+1145,490
+160,194
+912,410
+227,623
+1041,402
+811,257
+50,505
+67,772
+211,275
+751,38
+1078,311
+552,590
+1280,389
+1031,91
+102,654
+361,590
+50,241
+1225,445
+658,773
+1101,844
+785,89
+244,294
+984,564
+703,592
+430,493
+703,131
+214,345
+922,247
+706,35
+515,410
+724,560
+1113,325
+735,70
+1195,747
+244,136
+572,92
+1285,889
+813,227
+1245,591
+423,38
+962,708
+489,42
+865,687
+798,603
+271,777
+1299,854
+55,117
+885,182
+952,680
+1126,99
+129,275
+69,770
+1305,1
+65,683
+880,204
+224,142
+1235,151
+174,345
+1285,827
+1263,112
+1215,548
+50,884
+556,805
+288,147
+167,259
+47,434
+417,796
+609,54
+147,79
+848,385
+1305,451
+795,585
+569,472
+197,649
+837,371
+306,862
+924,863
+539,171
+1220,414
+909,749
+1041,191
+666,28
+716,128
+1091,613
+927,614
+686,120
+1200,98
+1255,466
+161,294
+952,438
+43,651
+445,739
+1235,781
+217,501
+42,371
+33,304
+386,863
+783,575
+999,304
+412,527
+239,591
+303,624
+622,794
+186,572
+785,469
+1213,712
+311,696
+459,240
+922,43
+694,523
+107,820
+1181,619
+1007,624
+454,847
+607,434
+1225,893
+393,795
+1113,693
+430,752
+388,549
+433,402
+115,723
+522,376
+713,624
+801,819
+884,145
+60,871
+823,259
+1263,24
+124,875
+601,725
+459,654
+1190,19
+1113,309
+1298,798
+1086,817
+1231,294
+919,551
+151,700
+539,536
+574,449
+544,546
+604,35
+569,422
+25,148
+1230,781
+587,351
+915,95
+1056,851
+1170,630
+915,150
+1278,100
+552,142
+132,518
+129,537
+1265,726
+410,316
+1285,372
+763,57
+11,563
+1076,348
+82,802
+977,256
+1260,35
+470,795
+1039,366
+388,345
+1225,870
+1208,240
+1016,346
+244,758
+254,851
+244,86
+1310,493
+567,71
+11,115
+1230,449
+711,565
+157,225
+856,847
+350,583
+694,595
+1267,651
+1115,128
+1110,47
+1233,333
+1208,654
+27,333
+845,665
+539,397
+445,687
+1041,703
+800,607
+960,535
+288,803
+165,294
+537,168
+186,322
+686,680
+1099,723
+607,302
+1101,626
+375,593
+525,201
+609,51
+373,207
+20,829
+157,618
+11,854
+139,36
+1009,596
+657,647
+410,578
+301,521
+348,186
+69,796
+1086,204
+771,210
+515,833
+924,31
+1288,359
+647,301
+949,749
+527,127
+1207,280
+689,23
+629,827
+661,767
+1034,483
+785,201
+500,851
+853,721
+1183,220
+735,824
+437,841
+959,624
+601,801
+1153,669
+224,369
+741,445
+457,721
+385,492
+1195,397
+828,267
+1039,152
+415,814
+785,581
+209,50
+1153,618
+25,827
+821,42
+271,614
+721,264
+1038,534
+900,561
+726,715
+1017,593
+795,36
+197,693
+758,240
+701,627
+557,438
+856,47
+497,359
+426,145
+594,128
+883,159
+1113,203
+604,211
+925,639
+927,329
+57,165
+807,331
+258,535
+905,2
+745,383
+629,789
+411,712
+348,513
+145,159
+80,449
+412,367
+922,269
+232,306
+415,815
+1014,774
+382,534
+950,324
+803,752
+243,182
+895,416
+395,346
+246,70
+657,695
+539,312
+455,660
+261,815
+386,31
+47,460
+816,194
+214,212
+599,117
+1186,875
+621,509
+845,682
+683,781
+415,192
+244,600
+157,807
+599,565
+909,348
+788,341
+102,401
+242,199
+718,623
+962,186
+77,674
+279,91
+884,537
+537,339
+430,401
+547,728
+706,57
+899,712
+233,210
+1054,133
+195,94
+234,800
+679,645
+845,821
+545,877
+597,624
+560,87
+768,72
+269,255
+723,351
+383,329
+1208,80
+233,236
+15,847
+704,136
+949,593
+1243,122
+321,451
+314,768
+1245,640
+1243,827
+1288,535
+1071,430
+612,875
+1220,480
+648,208
+758,752
+979,623
+1071,591
+542,212
+455,220
+89,511
+898,367
+415,863
+686,57
+127,212
+358,241
+937,504
+1113,17
+851,240
+343,752
+575,70
+366,539
+12,798
+229,357
+694,299
+698,75
+1260,505
+25,522
+1089,453
+358,438
+1150,194
+1184,847
+801,75
+851,128
+80,781
+1099,275
+1179,128
+582,704
+45,331
+38,299
+1073,369
+1242,670
+925,492
+259,772
+221,5
+209,319
+1245,683
+1179,318
+1250,542
+261,795
+1158,82
+161,714
+5,1
+1207,614
+783,569
+1205,624
+688,794
+890,240
+375,472
+502,68
+989,575
+428,159
+195,766
+689,749
+547,57
+299,113
+36,271
+1068,3
+1263,220
+888,588
+502,569
+917,99
+900,578
+47,220
+1081,357
+870,549
+237,749
+430,849
+1195,723
+900,310
+793,560
+741,449
+831,476
+433,492
+1073,322
+1086,369
+959,270
+334,686
+1228,362
+90,414
+507,367
+412,871
+851,352
+70,627
+33,509
+152,826
+539,582
+755,175
+405,450
+507,424
+528,47
+1165,159
+1032,360
+1250,871
+987,719
+932,483
+821,600
+566,777
+724,476
+1004,708
+937,275
+1086,33
+1073,145
+865,207
+1081,327
+358,689
+525,469
+261,192
+927,186
+0,401
+724,334
+127,767
+917,254
+709,93
+567,255
+361,369
+1171,36
+527,276
+527,679
+566,49
+726,267
+835,200
+373,619
+771,684
+445,851
+825,618
+465,821
+358,217
+1263,560
+406,115
+1200,460
+1082,593
+485,186
+923,485
+343,740
+426,357
+570,891
+274,236
+355,113
+165,376
+1081,771
+291,226
+877,889
+917,547
+480,569
+73,546
+782,847
+1195,312
+1295,847
+290,847
+55,466
+808,549
+209,626
+870,212
+433,876
+267,409
+1183,773
+1226,199
+22,359
+621,357
+229,119
+913,348
+160,700
+206,539
+534,19
+1041,553
+1159,3
+979,775
+291,312
+1113,245
+417,301
+282,551
+1203,389
+1029,267
+465,229
+1006,135
+1166,607
+1195,110
+880,401
+570,443
+733,333
+375,723
+137,560
+1173,560
+303,49
+930,210
+681,446
+209,844
+25,746
+1086,304
+1153,807
+1260,389
+296,205
+821,516
+935,723
+1082,145
+773,339
+32,346
+1263,782
+448,803
+853,247
+107,389
+68,476
+420,546
+793,334
+771,397
+694,803
+547,389
+977,319
+1039,565
+561,236
+559,184
+750,87
+1145,294
+490,621
+667,563
+661,443
+527,220
+862,467
+1022,91
+197,201
+171,705
+1155,637
+704,758
+50,35
+195,318
+882,735
+1242,476
+662,208
+855,212
+92,124
+248,442
+745,572
+858,691
+1086,861
+701,838
+348,750
+50,145
+877,453
+102,814
+50,859
+1241,796
+661,127
+271,117
+68,535
+231,548
+293,752
+440,613
+604,859
+929,568
+256,133
+587,515
+663,301
+920,495
+967,198
+228,593
+691,836
+1082,357
+835,246
+1129,147
+768,568
+808,180
+1203,148
+1310,655
+258,588
+837,819
+224,33
+490,273
+880,690
+715,840
+401,546
+1069,63
+542,568
+1285,334
+880,493
+1066,86
+1096,345
+736,449
+258,359
+1300,361
+724,418
+1227,264
+609,715
+152,549
+713,105
+373,838
+75,113
+475,246
+1200,796
+649,443
+552,752
+821,294
+32,324
+766,546
+708,658
+744,845
+272,534
+488,638
+795,484
+53,1
+219,515
+1113,761
+733,561
+853,581
+949,200
+60,493
+1228,84
+5,893
+185,633
+209,268
+877,18
+840,99
+331,775
+952,653
+197,17
+480,325
+171,854
+102,449
+937,723
+783,851
+711,728
+209,575
+517,334
+1029,627
+1081,119
+504,894
+427,159
+895,16
+181,747
+512,603
+701,54
+266,1
+338,740
+607,197
+155,637
+914,588
+324,213
+55,329
+1235,743
+169,276
+197,877
+1104,19
+179,470
+243,712
+602,658
+900,92
+393,99
+410,92
+1039,280
+1014,680
+994,861
+927,280
+253,301
+1233,561
+1044,549
+485,260
+589,470
+102,80
+507,143
+457,581
+706,837
+509,159
+1004,144
+415,366
+214,281
+237,572
+112,774
+920,399
+766,348
+324,325
+1260,859
+607,112
+900,802
+72,179
+830,569
+1161,710
+373,396
+269,639
+922,177
+714,843
+1135,292
+333,506
+90,480
+67,827
+1077,210
+596,843
+443,275
+820,273
+873,841
+1014,438
+306,144
+479,602
+987,327
+703,302
+552,829
+232,311
+1257,353
+393,264
+990,208
+12,96
+979,719
+497,667
+1007,270
+353,827
+947,668
+271,708
+221,453
+102,445
+221,402
+393,254
+1068,199
+253,266
+231,856
+1113,585
+731,319
+518,584
+301,821
+923,877
+147,815
+701,267
+1108,203
+329,292
+425,323
+986,213
+817,628
+1183,682
+72,715
+256,410
+475,200
+709,801
+564,414
+120,19
+459,352
+949,145
+390,399
+1044,585
+242,695
+445,50
+1046,399
+1044,43
+840,200
+206,19
+82,810
+67,351
+144,287
+304,135
+127,575
+1126,795
+566,397
+68,670
+624,241
+522,518
+1260,145
+1031,472
+244,578
+758,829
+223,17
+321,388
+624,568
+1086,466
+1235,878
+793,441
+165,742
+586,672
+564,480
+197,203
+294,548
+1268,371
+880,1
+629,446
+875,67
+1145,518
+415,519
+937,838
+1171,858
+425,771
+242,891
+721,303
+731,255
+82,767
+934,310
+383,614
+994,476
+1158,569
+22,535
+792,534
+1115,542
+1208,304
+1044,814
+959,497
+738,308
+855,220
+1043,409
+239,303
+47,91
+611,203
+
+fold along x=655
+fold along y=447
+fold along x=327
+fold along y=223
+fold along x=163
+fold along y=111
+fold along x=81
+fold along y=55
+fold along x=40
+fold along y=27
+fold along y=13
+fold along y=6
diff --git a/13/input_example.txt b/13/input_example.txt
new file mode 100644
index 0000000..282114c
--- /dev/null
+++ b/13/input_example.txt
@@ -0,0 +1,21 @@
+6,10
+0,14
+9,10
+0,3
+10,4
+4,11
+6,0
+6,12
+4,1
+0,13
+10,12
+3,4
+3,0
+8,4
+1,10
+2,14
+8,10
+9,0
+
+fold along y=7
+fold along x=5