#include <bits/stdc++.h>
using namespace std;
const int N = 5100;
char Map[N][N];
int dp[N][N];
int main() {
  int i, j;
  int line, row;
  scanf("%d%d", &line, &row);
  for (i = 0; i < line; i++) scanf("%s", Map[i]);
  for (i = 0; i < line; i++) {
    for (j = row - 1; j >= 0; j--) {
      if (Map[i][j] == '1')
        dp[j][i] = dp[j + 1][i] + 1;
      else
        dp[j][i] = 0;
    }
  }
  int ret = 0;
  for (i = 0; i < row; i++) {
    sort(dp[i], dp[i] + line);
    for (j = 0; j < line; j++) {
      ret = max(ret, (line - j) * dp[i][j]);
    }
  }
  printf("%d\n", ret);
  return 0;
}
