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def adjacent(coord, arr):
x, y = coord
max_x = len(arr[y]) - 1
max_y = len(arr) - 1
for dx in [-1, 0, 1]:
for dy in [-1, 0, 1]:
xp, yp = (x + dx, y + dy)
if ((xp, yp) == coord or min(xp, yp) < 0 or xp > max_x or yp > max_y):
continue
yield (xp, yp)
def flash(coord, arr, flashed):
flashed.add(coord)
for (x, y) in adjacent(coord, arr):
arr[y][x] += 1
visit((x, y), arr, flashed)
def visit(coord, arr, flashed):
x, y = coord
v = arr[y][x]
if v > 9 and coord not in flashed:
flash(coord, arr, flashed)
def step(arr):
flashed = set()
for (x,y) in ((x,y) for (y,l) in enumerate(arr) for (x,_) in enumerate(l)):
arr[y][x] = arr[y][x] + 1
visit((x,y), arr, flashed)
for (x,y) in flashed:
arr[y][x] = 0
return len(flashed)
def print_board(arr):
print("\n".join(["".join(map(str, l)) for l in arr]))
state = [[int(n) for n in l] for l in open("./input").read().strip().split("\n")]
total_squares = sum([len(l) for l in state])
n = 0
while True:
n += 1
if step(state) == total_squares:
break
print(n)
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