rhakdnsrhakdns

import copy

queue = []
def Bfs() :
    global N, M, H, day,queue,l
    p = 0
    le = len(queue)
    while len(queue) != 0 :
        if p == le :
            p = 0
            day += 1
            le = len(queue)
        q = queue.pop(0)
        p += 1
        if q[0]+1 < H and l[q[0]+1][q[1]][q[2]] == 0 :
            queue.append([q[0]+1, q[1], q[2]])
            l[q[0]+1][q[1]][q[2]] = 1
        if q[0]-1 >= 0 and l[q[0]-1][q[1]][q[2]] == 0 :
            queue.append([q[0]-1, q[1], q[2]])
            l[q[0]-1][q[1]][q[2]] = 1
        if q[1]+1 < N and l[q[0]][q[1]+1][q[2]] == 0 :
            queue.append([q[0], q[1]+1, q[2]])
            l[q[0]][q[1]+1][q[2]] = 1
        if q[1]-1 >= 0 and l[q[0]][q[1]-1][q[2]] == 0 :
            queue.append([q[0], q[1]-1, q[2]])
            l[q[0]][q[1]-1][q[2]] = 1
        if q[2]+1 < M and l[q[0]][q[1]][q[2]+1] == 0 :
            queue.append([q[0], q[1], q[2]+1])
            l[q[0]][q[1]][q[2]+1] = 1
        if q[2]-1 >= 0 and l[q[0]][q[1]][q[2]-1] == 0 :
            queue.append([q[0], q[1], q[2]-1])
            l[q[0]][q[1]][q[2]-1] = 1


l = []
tl= []
day = 0
M, N, H = map(int, input().split())
for j in range(H) :
    for i in range(N) :
        v = list(map(int, input().split()))
        tl.append(v)
    l.append(copy.deepcopy(tl))
    tl.clear()

for y in range(H) :
    for z in range(N) :
        for x in range(M) :
            if l[y][z][x] == 1 :
                queue.append([y, z, x])
                l[y][z][x] = 1

Bfs()
for y in range(H) :
    for z in range(N) :
        for x in range(M) :
            if l[y][z][x] == 0 :
                print(-1)
                exit()
            else :
                print(day)
                exit()