#include <bits/stdc++.h>
using namespace std;
const int N = 5005;
const int inf = 1000000005;
int n, m, r[N][N];
char str[N][N];
int main() {
  scanf("%d %d", &n, &m);
  for (int i = 1; i <= n; i++) {
    scanf("%s", str[i] + 1);
  }
  for (int i = 1; i <= n; i++) {
    for (int j = m; j >= 1; j--) {
      if (str[i][j] == '0')
        r[i][j] = 0;
      else
        r[i][j] = r[i][j + 1] + 1;
    }
  }
  int ans = 0;
  for (int j = m; j >= 1; j--) {
    vector<int> v;
    for (int i = 1; i <= n; i++) {
      v.push_back(r[i][j]);
    }
    sort(v.begin(), v.end());
    reverse(v.begin(), v.end());
    for (int i = 0; i < v.size(); i++) {
      ans = max(ans, v[i] * (i + 1));
    }
  }
  printf("%d\n", ans);
  return 0;
}
