#include<bits/stdc++.h>
using namespace std;
const int maxn = 1000;
int a[maxn][maxn];
int main(){
    int n, m;
    cin >> n >> m;
    for(int i = 0; i < n; i++){
        string s;
        cin >> s;
        for(int j = 1; j < m; i++){
            a[i][j] = s[j]-'0';
        }
    }
        int maxnn = 0, b = 0, c = 0;
        for(int k = 0; k < n; k++){
            for(int u = k; u < n; u++){
                for(int l = 0; l < m; l++){
                    for(int h = 0; h < m; h++){
                        for(int d = k; d <= l; d++){
                            if(a[l][h] == 0){
                                c++;
                            }else{
                                b++;
                            }                 
                        }
                        if(b == c){
                        int r = (h-k+1)*(h-l+1);
                        maxnn = max(maxnn,r);
                    }
                    }
                    
                }
            }
    }
    cout << maxnn << endl;
    return 0;
}