#include <cstdio>
#include <queue>
using namespace std;
#define Flag 10000000
struct Point {
int x, y, z;
};
int width, height, length;
int map[100][100][100];
queue<Point> que;
int cnt;
Point make_Point(int z, int y, int x) {
Point p;
p.z = z;
p.y = y;
p.x = x;
return p;
}
int bfs()
{
Point p;
int dz[6] = { -1, 1, 0, 0, 0, 0 };
int dy[6] = { 0, 0, -1, 1, 0, 0 };
int dx[6] = { 0, -0, 0, 0, -1, 1 };
while (!que.empty()) {
p = que.front();
que.pop();
for (int i = 0; i < 6; i++) {
Point next = make_Point(p.z + dz[i], p.y + dy[i], p.x + dx[i]);
if (next.z >= 0 && next.z < length && next.y >= 0
&& next.y < height && next.x >= 0 && next.x < width) {
if (map[next.z][next.y][next.x] == 0) {
map[next.z][next.y][next.x] = map[p.z][p.y][p.x] + 1;
que.push(next);
cnt--;
}
}
}
}
if (cnt <= 0) return map[p.z][p.y][p.x] - Flag - 1;
return -1;
}
int main()
{
scanf("%d %d %d", &width, &height, &length);
for (int z = 0; z < length; z++) {
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
scanf("%d", &map[z][y][x]);
if (map[z][y][x] == 1) {
que.push(make_Point(z, y, x));
map[z][y][x] += Flag;
}
else if (map[z][y][x] == 0) cnt++;
}
}
}
printf("%d\n", bfs());
return 0;
}
