#include <bits/stdc++.h>
const double EPS = 1e-24;
const long long int MOD = 1000000007ll;
const double PI = 3.14159265359;
int INF = 2147483645;
template <class T>
T Max2(T a, T b) {
  return a < b ? b : a;
}
template <class T>
T Min2(T a, T b) {
  return a < b ? a : b;
}
template <class T>
T Max3(T a, T b, T c) {
  return Max2(Max2(a, b), c);
}
template <class T>
T Min3(T a, T b, T c) {
  return Min2(Min2(a, b), c);
}
template <class T>
T Max4(T a, T b, T c, T d) {
  return Max2(Max2(a, b), Max2(c, d));
}
template <class T>
T Min4(T a, T b, T c, T d) {
  return Min2(Min2(a, b), Max2(c, d));
}
template <class T>
void Swap(T& a, T& b) {
  T temp;
  temp = a;
  a = b;
  b = temp;
}
using namespace std;
int N, M;
string s[5010];
int r[5010][5010];
int main() {
  std::ios::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> N >> M;
  for (int i = 0; i < N; i++) cin >> s[i];
  for (int i = 0; i < N; i++) {
    if (s[i][M - 1] == '0')
      r[i][M - 1] = 0;
    else
      r[i][M - 1] = 1;
    for (int j = M - 2; j >= 0; j--) {
      if (s[i][j] == '0')
        r[i][j] = 0;
      else
        r[i][j] = r[i][j + 1] + 1;
    }
  }
  int ans = -1;
  for (int j = 0; j < M; j++) {
    vector<int> v;
    for (int i = 0; i < N; i++) v.push_back(r[i][j]);
    sort(v.begin(), v.end());
    for (int i = 0; i < N; i++) ans = Max2(ans, v[i] * (N - i));
  }
  cout << ans;
  return 0;
}
