#include <bits/stdc++.h>

using namespace std;
const int N = 110;
int n, m;
int a[N][N], s[N][N];
int res;
int main() {
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++) {
            cin >> a[i][j];
            a[i][j] = !a[i][j];
            s[i][j] = s[i - 1][j] + s[i][j - 1] - s[i - 1][j - 1] - a[i][j];
        }
    for (int x1 = 1; x1 <= n; x1++)
        for (int y1 = 1; y1 <= m; y1++)
            for (int x2 = x1 + 1; x2 <= n; x2++)
                for (int y2 = y1 + 1; y2 <= m; y2++) {
                    int sum = s[x2][y2] - s[x1 - 1][y2] - s[x2][y1 - 1] + s[x1 - 1][y1 - 1];
                    if ((x2 - x1 + 1) * (y2 - y1 + 1) == sum)
                        res = max(res, sum);
                }
    printf("%d\n", res);
    return 0;
}