#include<bits/stdc++.h>
#define pii pair<int,int>
#define ff first
#define ss second
 
using namespace std;
 
bool color[505][505];
 
char arr[505][505];
 
int dist[505][505],m;
 
int x[] = {-1,+1,0,0};
 
int y[] = {0,0,+1,-1};
 
bool check(int r,int c)
{
    if(r>=0 && r<m && c>=0 && c<m)
        return true;
 
    return false;
}
 
int bfs(pii source)
{
    memset(color,false,sizeof color);
 
    memset(dist,-1,sizeof dist);
 
    color[source.ff][source.ss] = true;
 
    dist[source.ff][source.ss] = 0;
 
    queue<pii>Q;
 
    Q.push(source);
 
    while(!Q.empty())
    {
        pii now = Q.front();
 
        Q.pop();
 
        if(arr[now.ff][now.ss]=='3')
        {
            return dist[now.ff][now.ss];
        }
 
        int i,r,c;
 
        for(i=0; i<4; i++)
        {
            r = x[i]+now.ff;
 
            c = y[i]+now.ss;
 
            if(check(r,c) && !color[r][c])
            {
                color[r][c] = true;
 
                dist[r][c] = dist[now.ff][now.ss]+1;
 
                Q.push(make_pair(r,c));
            }
        }
    }
}
 
int main()
{
    int i,j,res;
 
    while(scanf("%d",&m)==1)
    {
        getchar();
 
        for(i=0; i<m; i++)
        {
            gets(arr[i]);
        }
 
        res = 0;
 
        for(i=0; i<m; i++)
        {
            for(j=0; j<m; j++)
            {
                if(arr[i][j]=='1')
                {
                    res = max(res,bfs(make_pair(i,j)));
                }
            }
        }
 
        printf("%d\n",res);
 
    }
 
    return 0;
}