#include <bits/stdc++.h>
using namespace std;
int l,w,n,m,a[1010][1010],s[1010][1010],ans;
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 bc=1;bc<=min(n,m);bc++){
		for(int i=1;i+bc-1<=n;i++){
			for(int j=1;j+bc-1<=m;j++){
				if(bc*bc==s[i+bc-1][j+bc-1]-s[i-1][j+bc-1]-s[i+bc-1][j-1]+s[i-1][j-1]){
					ans=max(ans,bc);
				}
			}
		}
	}
	cout<<ans;
	return 0;
}