#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<vector>
using namespace std;
int cou[5005][5005]={0};
char t[5005];
int main()
{
  int n,m;
  freopen(".20.in","r",stdin);
  freopen(".20.out","w",stdout);
  int i,j,s;
  int ans=0;
  cin>>n>>m;
  for(i=1;i<=n;i++)
  {
    scanf("%s",t);
    s=0;
    for(j=0;j<m;j++)
    {
      if(t[j]=='0')
        s=j+1;
      else
        cou[s][j]++;
    }
  }
  for(i=2;i<m;i++)
    for(j=1;j<=i;j++)
      cou[j][i]+=cou[j-1][i];
  for(i=0;i<m;i++)
    for(j=i;j<m;j++)
      ans=max(ans,(j-i+1)*cou[i][j]);
  cout<<ans<<endl;
  return 0;
}