#include <bits/stdc++.h>
using namespace std;
const int inf = 1e9;
int n, m;
char a[5555][5555];
int r[5555][5555];
int c[5555];
int ans = 0;
int main() {
  int i, j;
  cin >> n >> m;
  for (i = 1; i <= n; ++i) {
    getchar();
    for (j = 1; j <= m; ++j) {
      a[i][j] = getchar();
    }
  }
  for (i = n; i >= 1; --i)
    for (j = m; j >= 1; --j) {
      if (a[i][j] == '0')
        r[i][j] = 0;
      else
        r[i][j] = r[i][j + 1] + 1;
    }
  for (j = 1; j <= m; ++j) {
    int k = 0;
    for (i = 1; i <= m; ++i) {
      c[i] = 0;
    }
    for (i = 1; i <= n; ++i) {
      c[r[i][j]]++;
      if (r[i][j]) k++;
    }
    for (i = 1; i <= m; ++i) {
      if (c[i]) ans = max(ans, i * k);
      k -= c[i];
    }
  }
  cout << ans;
  return 0;
}
