#include<iostream>

#include<cstdio>

#include<cstring>

#include<string>

#include<algorithm>

#include<cctype>

#include<cmath>

#include<cstdlib>

#include<queue>

#include<ctime>

#include<vector>

#include<set>

#include<map>

#include<stack>

using namespace std;

int n,m,g[][],f[][],d[],ans,res;

int main(){

    int i,j,k;

    scanf("%d%d",&n,&m);

    for(i=;i<=n;i++)

      for(j=;j<=m;j++)

        scanf("%d",&g[i][j]);

    for(i=;i<=n;i++)

      for(j=;j<=m;j++)

        f[i][j]=(g[i][j]?f[i][j-]+:);

    for(i=;i<=m;i++){

      for(j=;j<=n;j++)d[j]=f[j][i];

      sort(d+,d+n+);

      for(j=;j<=n;j++)

        res=max(res,(n-j+)*d[j]);

      ans=max(ans,res);

    }

    cout<<ans<<"\n";

    return ;

}