#include<bits/stdc++.h>
using namespace std;
const int N=130;
int a[N][N],s[N][N],n,cnt,m;
bool b=true;
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]+a[i][j]-s[i-1][j-1];
		}
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			for(int i2=1;i2<=n;i2++){
				if(s[i+i2][j+i2]-s[i-1][j+i2]-s[i+i2][j-1]+s[i-1][j-1]==i2*i2){
					cnt=i2;
				}
			}
		}
	}
	cout<<cnt;
	return 0;
}