diff --git a/2021/day13.py b/2021/day13.py
new file mode 100644
index 0000000..9953052
--- /dev/null
+++ b/2021/day13.py
@@ -0,0 +1,31 @@
+with open("input13.txt") as f:
+    coords = []
+    folds = []
+    for line in map(str.rstrip, f):
+        if "," in line:
+            coords.append(tuple(map(int, line.split(","))))
+        elif line and line[0] == "f":
+            c, v = line.rsplit(maxsplit=1)[-1].split("=")
+            folds.append((c == "x", int(v)))
+
+for i, (is_h, v) in enumerate(folds):
+    if is_h:
+        coords = set(
+            (x - (x - v) * 2, y) if x > v else (x, y)
+            for x, y in coords
+        )
+    else:
+        coords = set(
+            (x, y - (y - v) * 2) if y > v else (x, y)
+            for x, y in coords
+        )
+    if i == 0:
+        print(len(coords))
+
+dx = max(coords, key=lambda p: p[0])[0] + 1
+dy = max(coords, key=lambda p: p[1])[1] + 1
+screen = [[" "] * dx for _ in range(dy)]
+for x, y in coords:
+    screen[y][x] = "█"
+for row in screen:
+    print("".join(row))