#17 WA
#include <iostream>
using namespace std;
char a[11][11];
bool x(int sx, int sy, int fx, int fy) {
int sum = (fx - sx + 1) * (fy - sy + 1);
int cnt = 0;
for (int i = sx; i <= fx; i++) {
for (int j = sy; j <= fy; j++) {
if (a[i][j] == '0') {
cnt++;
}
}
}
return sum - cnt == cnt;
}
int main() {
int n, m;
cin >> n >> m;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
cin >> a[i][j];
}
}
int maxx = 0;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= n; j++) {
for (int k = i; k <= n; k++) {
for (int l = j; l <= m; l++) {
if(x(i, j, k, l)) {
int sum = (k - i + 1) * (l - j + 1);
maxx = max(maxx, sum);
}
}
}
}
}
cout << maxx;
return 0;
}