diff --git a/day23/input b/day23/input
new file mode 100644
index 0000000..7bedbaf
--- /dev/null
+++ b/day23/input
@@ -0,0 +1,72 @@
+#.#####..#..##......##.#..####....#.#.####..##.#######..##..##.###...#..
+..#..##.#.#.#.##.#......######.#...###....#....#.#..#####.....#..#.####.
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diff --git a/day23/sample1.in b/day23/sample1.in
new file mode 100644
index 0000000..14005cf
--- /dev/null
+++ b/day23/sample1.in
@@ -0,0 +1,7 @@
+....#..
+..###.#
+#...#.#
+.#...##
+#.###..
+##.#.##
+.#..#..
diff --git a/day23/sol.py b/day23/sol.py
new file mode 100644
index 0000000..6161270
--- /dev/null
+++ b/day23/sol.py
@@ -0,0 +1,84 @@
+from collections import Counter
+pos = {}
+y = 0
+for line in open("input"):
+    for x, c in enumerate(line):
+        if c == '#':
+            pos[x,y] = 1
+    y += 1
+
+
+def choices(pos, dir):
+    x,y = pos
+    dy = (dir == 'S') - (dir == 'N')
+    dx = (dir == 'E') - (dir == 'W')
+    if dx:
+        for dy in -1,0,+1:
+            yield x+dx,y+dy
+    else:
+        assert dy
+        for dx in -1,0,+1:
+            yield x+dx, y+dy
+
+def go(pos, dir):
+    x,y = pos
+    dy = (dir == 'S') - (dir == 'N')
+    dx = (dir == 'E') - (dir == 'W')
+    return x+dx,y+dy
+
+def neighbors(pos):
+    x,y = pos
+    for dx in -1,0,+1:
+        for dy in -1,0,+1:
+            if dx or dy:
+                yield x+dx,y+dy
+
+def migrate(start, rounds):
+    moves = ['N', 'S', 'W', 'E']
+    for _ in range(rounds):
+        show(start)
+        print("-")
+        propose = {}
+        destCount = Counter()
+
+        for p in start:
+            propose[p] = p
+            if any(n in start for n in neighbors(p)):
+                for m in moves:
+                    if not any(c in start for c in choices(p, m)):
+                        c = go(p,m)
+                        propose[p] = c
+                        destCount[c] += 1
+                        break
+
+        next = {}
+        for p, d in propose.items():
+            if destCount[d] <= 1:
+                next[d] = 1
+            else:
+                next[p] = 1
+
+        moves.append(moves.pop(0))
+        start = next
+    return start
+
+def show(pos):
+    xmin = min(x for x,y in pos)
+    ymin = min(y for x,y in pos)
+    xmax = max(x for x,y in pos)
+    ymax = max(y for x,y in pos)
+    for y in range(ymin, ymax+1):
+        print("".join(".#"[(x,y) in pos] for x in range(xmin,xmax+1)))
+
+def count_empty(pos):
+    n = 0
+    xmin = min(x for x,y in pos)
+    ymin = min(y for x,y in pos)
+    xmax = max(x for x,y in pos)
+    ymax = max(y for x,y in pos)
+    return (ymax-ymin+1)*(xmax-xmin+1) - len(pos)
+
+
+#print(pos)
+n = count_empty(migrate(pos, 10))
+print(n)