C++ :

#include <algorithm>
#include <cstdio>
using namespace std;
const int N = 15;
int n, m;
int a[N][N];
int ans;
int main() {
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= m; j++) scanf("%d", &a[i][j]);
	for (int u = 1; u <= n; u++)
		for (int l = 1; l <= m; l++)
			for (int d = u; d <= n; d++) {
				int chk = 1;
				for (int r = l; r <= m; r++) {
					for (int x = u; x <= d; x++) chk &= a[x][r];
					if (!chk) break;
					ans = max(ans, (r - l + 1) * (d - u + 1));
				}
			}
	printf("%d\n", ans);
	return 0;
}