#include<bits/stdc++.h>
using namespace std;
const int N=101;
int n,m;
int a[N][N],b[N][N],s[N][N];
void solve()
{
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=m;j++)
		{
			s[i][j]=s[i-1][j]+s[i][j-1]-s[i-1][j-1]+a[i][j];
		}
	}
	int ans=0;
		for(int x1=1;x1<=n;x1++)
		{
			for(int x2=1;x2<=n;x2++)
			{
				if(x1>=x2)continue;
				for(int y1=1;y1<=m;y1++)
				{
					for(int y2=1;y2<=m;y2++)
					{
					if(y1>=y2)continue;
					b[x2][y2]=s[x2][y2]-s[x2][y1-1]-s[x1-1][y2]+s[x1-1][y1-1];
					if(b[x2][y2]==(x2-x1+1)*(x2-x1+1)&&x2-x1>ans) ans=x2-x1+1;
					}
				}
			}
		}
cout<<ans;				
}
int main()
{
cin>>n>>m;
for(int i=1;i<=n;i++)
{
	for(int j=1;j<=m;j++)
	{
	cin>>a[i][j];	
	}
}
solve();
	return 0;
 }