#include<bits/stdc++.h>
using namespace std;
const int N=205;
int hsus[N][N];
int hjos[N][N];
char mat[N][N];
int stv[N];
int st[N];
int skyline(int v[],int n){
  int vf=0;
  for(int i=1;i<=n;i++){
    while(vf>0 && v[i]<=v[stv[vf]])
      vf--;
    st[i]=stv[vf];
    stv[++vf]=i;
  }
  int ans=0;
  vf=0;
  stv[vf]=n+1;
  for(int i=n;i>=1;i--){
    while(vf>0 && v[i]<=v[stv[vf]])
      vf--;
    int dr=stv[vf];
    ans=max(ans,(dr-st[i]-1)*v[i]);
    stv[++vf]=i;
  }
  return ans;
}
int main()
{
  FILE*fin,*fout;
  fin=fopen("bmax.in","r");
  fout=fopen("bmax.out","w");
  int n,m;
  fscanf(fin,"%d%d",&n,&m);
  for(int i=1;i<=n;i++){
    fgets(mat[i]+1,N,fin);
    for(int j=1;j<=m;j++)
      mat[i][j]-='0';
  }
  for(int i=1;i<=n;i++){
    for(int j=1;j<=m;j++){
      if(mat[i][j]==0){
        hsus[i][j]=hsus[i-1][j]+1;
      }
      else
        hsus[i][j]=0;
    }
  }
  for(int i=n;i>=1;i--){
    for(int j=1;j<=m;j++){
      if(mat[i][j]==0){
        hjos[i][j]=hjos[i+1][j]+1;
      }
      else
        hjos[i][j]=0;
    }
  }
  int ans=0;
  for(int lin=1;lin<=n;lin++){
    ans=max(ans,skyline(hsus[lin],m)+skyline(hjos[lin+1],m));
  }
  fprintf(fout,"%d",ans);
  return 0;
}