文献：https://blog.csdn.net/wesigj/article/details/108959219?utm_medium=distribute.pc_aggpage_search_result.none-task-blog-2~aggregatepage~first_rank_ecpm_v1~rank_v31_ecpm-1-108959219.pc_agg_new_rank&utm_term=stringstream+%E4%B8%ADssin&spm=1000.2123.3001.4430
题目：https://www.acwing.com/problem/content/description/730/

//输入很有特色

#include<iostream>
#include<cstring>
#include<queue>
#include<sstream>

using namespace std;

const int N = 15;
typedef pair<int,int>PII;
typedef pair<PII,int>PIII;

int dx[] = {0, 1, 0, -1}, dy[] = {1 , 0, -1, 0};
int g[N][N];

int n, m;

int bfs(){
    int val = 0;
    int start = 0;
    int end = 0;
    queue<PIII>q;
    for(int i = 0; i < n; i ++ )
        for(int j = 0; j < m; j ++ )
            if(g[i][j] == 2)    q.push({{i, j}, 0});
            else if(g[i][j] == 1)   start ++;
    while(q.size()){
        auto u = q.front();
        q.pop();
        PII uu = u.first;
        int x = uu.first, y = uu.second, dist = u.second;
        val = dist;
        for(int i = 0; i < 4; i ++ ){
            int a = dx[i] + x, b = dy[i] + y;
            if(a >= 0 && b >= 0 && a < n && b < m && g[a][b] == 1){
                q.push({{a, b}, dist + 1});
                g[a][b] = 2;
                end ++;
            }
        }
    }
    if(start == end)   return val;    
    return -1;
}

int main(){
    string line;
    while(getline(cin, line)){
        stringstream s(line);
        int k = 0;
        while(s >> g[n][k]) k ++;   
        m = k;
        n ++;
    }
    cout<<bfs();
    return 0;
}