# 시간 초과되는지 처음 알았다...
import sys
input = sys.stdin.readline
import sys
from collections import deque
M, N, H = map(int, sys.stdin.readline().split())
boxes = [[list(map(int, sys.stdin.readline().split())) for _ in range(N)] for _ in range(H)]
dx = [-1, 1, 0, 0, 0, 0]
dy = [0, 0, -1, 1, 0, 0]
dh = [0, 0, 0, 0, -1, 1]
q = deque()
for h in range(H):
for n in range(N):
for m in range(M):
if boxes[h][n][m] == 1:
q.append([h, n, m])
while q:
h, x, y = q.popleft()
for d in range(6):
nh = h + dh[d]
nx = x + dx[d]
ny = y + dy[d]
if 0 <= nh < H and 0 <= nx < N and 0 <= ny < M and boxes[nh][nx][ny] == 0:
boxes[nh][nx][ny] = boxes[h][x][y] + 1
q.append([nh, nx, ny])
day = 0
for h in boxes:
for m in h:
for n in m:
if n == 0:
day = 0
break
day = max(day, n)
else:
continue
break
else:
continue
break
print(day-1)