qbsquare

//#include<bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<fstream>

#define long long long
#define nln '\n'

const long N = 1e3 + 10;

using namespace std;

// Global variables: n, m, mat

long n, m, dp[N][N], ans = -1;
bool mat[N][N];
fstream f1;

bool above(long i, long j)
{
    if (i == 1)
        return 0;
    if (mat[i][j] == mat[i-1][j])
        return 1;
    return 0;
}

bool left(long i, long j)
{
    if (j == 1)
        return 0;
    if (mat[i][j] == mat[i][j-1])
        return 1;
    return 0;
}

bool cross(long i, long j)
{
    if (i == 1 || j == 1)
        return 0;
    if (mat[i][j] == mat[i-1][j-1])
        return 1;
    return 0;
}

int main()
{
    cin >> m >> n;
    for (long i = 1; i <= m; ++i)
        for (long j = 1; j <= n; ++j)
        {
            cin >> mat[i][j];
            dp[i][j] = 1;
            if (cross(i, j) && above(i, j) && left(i, j))
                dp[i][j] = min(min(dp[i-1][j], dp[i-1][j-1]), dp[i][j-1]) + 1;
            if (dp[i][j] > ans)
                ans = dp[i][j];
        }
    cout << ans << nln;
    return 0;
}