#include<bits/stdc++.h>
using namespace std;
int n,m,ans=0; 
struct node{
	char num;
	int qs;
}a[15][15];
int main(){
    cin>>n>>m;
    for (int i=1;i<=n;i++){
    	for (int j=1;j<=m;j++){
    		cin>>a[i][j].num;
    		if (j!=1) a[i][j].qs=a[i][j-1].qs+(a[i][j].num-'0');
    		else a[i][j].qs=a[i-1][m].qs+(a[i][j].num-'0');
		}
	}
	for (int i=1;i<=n;i++){
		for (int j=1;j<=m;j++){
			for (int x=1;x<=n;x++){
				for (int y=1;y<=m;y++){
					if (a[i][j].qs-a[x][y].qs==(m-j+1)*(n-x+1)/2) ans=max(ans,(m-j+1)*(n-x+1));
				}
			}
		}
	} 
	cout<<ans;
	return 0;
}