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#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <climits>
using namespace std;

template <typename T>
class Queue {
    int start, end;
    vector<T> v;
    public:    
    Queue() {
        start = 0;
        end = 0;
    }
    void push(T e) {
        v.push_back(e);
        end++;
    }
    bool empty() {
        return start == end;
    }
    T front() {
        return v[start];
    }
    void pop() {
        start++;
    }
    int size() {
        return end - start;
    }
};

class Pair {
    public:
    int F, S;
};

int main() {
    int m, n, minute = 0; cin >> m >> n;
    int grid[m][n];
    int dx[] = {-1, 1, 0, 0};
    int dy[] = {0, 0, -1, 1};
    Queue<Pair> q;
    for(int i = 0; i < m; i++) {
        for(int j = 0; j < n; j++) {
            cin >> grid[i][j];
            if(grid[i][j] == 2) {
                q.push({i, j});
            }
        }
    }
    q.push({-1, -1});

    while(!q.empty()) {
        Pair p = q.front(); q.pop();
        if (p.F == -1 && p.S == -1) {
            if(q.size() >= 1) {
                minute++;
                q.push({-1, -1});
                continue;
            }
            else break;
        }
        for(int i = 0; i < 4; i++) {
            int x = p.F + dx[i], y = p.S + dy[i];
            if(x < 0 || x >= m || y < 0 || y >= n) continue;
            if(grid[x][y] == 2 || grid[x][y] == 0) continue;
            grid[x][y] = 2;
            q.push({x, y});
        }
    }

    for(int i = 0; i < m; i++) {
        for(int j = 0; j < n; j++) {
            if(grid[i][j] == 1) {
                minute = -1;
                break;
            }
        }
    }
    cout << minute << "\n";
    return 0;
}