import sys
from collections import deque

input = sys.stdin.readline

N, M, H = map(int, input().split())
visited = [[[-1]*N for _ in range(M)] for _ in range(H)]
emptyCount = 0
visitCount = 0
q = deque()

tomato = []
for z in range(H):
    tomato.append([])
    for y in range(M):
        row = list(map(int, input().split()))
        tomato[z].append(row)
        for x in range(N):
            if row[x] == 1 :
                q.append((z,y,x))
                visited[z][y][x] = 0
                visitCount += 1
            
            elif row[x] == -1 :
                emptyCount += 1


dx = [1,-1,0,0,0,0]
dy = [0,0,1,-1,0,0]
dz = [0,0,0,0,1,-1]
dayMax = 0

while len(q) :
    cz, cy, cx = q.popleft()
        
    for i in range(6):
        nz, ny, nx = cz + dz[i], cy + dy[i], cx + dx[i]
        if 0<=nz<H and 0<=ny<M and 0<=nx<N and visited[nz][ny][nx] == -1 and tomato[nz][ny][nx] == 0:
            q.append((nz,ny,nx))
            visitCount += 1
            visited[nz][ny][nx] = visited[cz][cy][cx] + 1
            if visited[nz][ny][nx] > dayMax :
                dayMax = visited[nz][ny][nx]
    
if N*M*H == visitCount + emptyCount :
    print(dayMax)
else :
    print(-1)