#include <bits/stdc++.h>
using namespace std;
long long Set(long long N, long long pos) { return N = N | (1 << pos); }
long long reset(long long N, long long pos) { return N = N & ~(1 << pos); }
bool check(long long N, long long pos) { return (bool)(N & (1 << pos)); }
void CI(long long &_x) { scanf("%I64d", &_x); }
void CO(long long &_x) { cout << _x; }
template <typename T>
void getarray(T a[], long long n) {
  for (long long i = 0; i < n; i++) cin >> a[i];
}
template <typename T>
void prLLIarray(T a[], long long n) {
  for (long long i = 0; i < n - 1; i++) cout << a[i] << " ";
  cout << a[n - 1] << endl;
}
const double EPS = 1e-9;
const long long INF = 0x7f7f7f7f;
long long dr8[8] = {1, -1, 0, 0, 1, -1, -1, 1};
long long dc8[8] = {0, 0, -1, 1, 1, 1, -1, -1};
long long dr4[4] = {0, 0, 1, -1};
long long dc4[4] = {-1, 1, 0, 0};
long long kn8r[8] = {1, 2, 2, 1, -1, -2, -2, -1};
long long kn8c[8] = {2, 1, -1, -2, -2, -1, 1, 2};
char grid[5005][5005];
int arr[5005][5005];
int rightt[5005][5005];
int main() {
  int n, m;
  cin >> n >> m;
  for (long long i = 1; i <= n; i++) scanf("%s", grid[i] + 1);
  for (long long i = 1; i <= n; i++) {
    int sum = 0;
    for (long long j = 1; j <= m; j++)
      if (grid[i][j] == '1')
        arr[i][j] = 1 + arr[i][j - 1];
      else
        arr[i][j] = 0;
  }
  for (int j = 1; j <= m; j++)
    for (int i = 1; i <= n; i++) {
      rightt[j][i] = arr[i][j];
    }
  for (int j = 1; j <= m; j++) {
    sort(rightt[j] + 1, rightt[j] + n + 1);
  }
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++) ans = max(ans, (n - i + 1) * rightt[j][i]);
  }
  cout << ans << "\n";
}
