#include <bits/stdc++.h>
#define N 105
using namespace std;
typedef long long ll;
int a[N][N], n, m, s[N][N] = {0}, ans = 0;
int main()
{
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= m; j++)
        {
            cin >> a[i][j];
            s[i][j] = s[i - 1][j] + s[i][j - 1] - s[i - 1][j - 1] + a[i][j];
        }
    }
    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= m; j++)
        {
            for (int l = 0; l < n - max(i, j); l++)
            {
                if (s[i + l][j + l] - s[i + l][j - 1] - s[i - 1][j + l] + s[i - 1][j - 1] == (l + 1) * (l + 1) && l + 1 > ans)
                {
                    ans = l + 1;
                }
            }
        }
    }
    cout << ans << endl;
    return 0;
}