#include <stdio.h>
#define MAX 100
#define INFI 9999999
typedef struct _Pos {
int x;
int y;
int c;
} Pos;
Pos pos[INFI];
int front = -1, rear = -1;
int number = 1;
int map[MAX][MAX];
int visited[MAX][MAX];
int px[] = {-1, 1, 0, 0};
int py[] = {0, 0, -1, 1};
void initVisitedMap () {
for (int y = 0; y < MAX; y++) {
for (int x = 0; x < MAX; x++) {
visited[y][x] = 0;
}
}
}
void setLandNumber (int x, int y, int n, int limit) {
map[y][x] = n;
visited[y][x] = 1;
for (int i = 0; i < 4; i++) {
int newX = x + px[i];
int newY = y + py[i];
if (newX < 0 || newX >= limit || newY < 0 || newY >= limit) {
continue;
}
if (!visited[newY][newX] && map[newY][newX] > 0) {
setLandNumber(newX, newY, n, limit);
}
}
}
int getMinLandCost (int n, int limit) {
int min = INFI;
for (int y = 0; y < limit; y++) {
for (int x = 0; x < limit; x++) {
if (map[y][x] == n) {
rear++;
pos[rear].x = x;
pos[rear].y = y;
pos[rear].c = 0;
}
}
}
while (front < rear) {
front++;
int x = pos[front].x;
int y = pos[front].y;
int c = pos[front].c;
for (int i = 0; i < 4; i++) {
int newX = x + px[i];
int newY = y + py[i];
if (newX < 0 || newX >= limit || newY < 0 || newY >= limit) {
continue;
}
if (map[newY][newX] != 0 && map[newY][newX] != n) {
if (min > c) {
min = c;
break;
}
} else if (map[newY][newX] == 0 && !visited[newY][newX]) {
rear++;
pos[rear].x = newX;
pos[rear].y = newY;
pos[rear].c = newC + 1;
visited[newY][newX] = 1;
}
}
}
return min;
}
int main(void) {
int N = 0;
int Min = INFI;
scanf("%d", &N);
for (int y = 0; y < N; y++) {
for (int x = 0; x < N; x++) {
scanf("%d", &map[y][x]);
}
}
for (int y = 0; y < N; y++) {
for (int x = 0; x < N; x++) {
if (map[y][x] > 0 && !visited[y][x]) {
setLandNumber(x, y, number, N);
number++;
}
}
}
initVisitedMap();
for (int i = 0; i < number; i++) {
int minPath = getMinLandCost(i + 1, N);
if (Min > minPath) {
Min = minPath;
}
rear = -1;
front = -1;
initVisitedMap();
}
printf("%d\n", (Min == INFI) ? 0 : Min);
return 0;
}
