#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int a[205][205],n,m,s[205],d[205],stiva[205],v[205][205],nr,mat[205][205],arie1=0,arie2=0,l1,l2,c1,c2;
char ata[205][205];
int main()
{
ifstream f("bmatrix.in");
ofstream g("bmatrix.out");
f>>n>>m;
for(int i=1;i<=n;i++)
  for(int j=1;j<=m;j++)
 {
  f>>ata[i][j];
  if(ata[i][j]=='0') a[i][j]=0;
  else a[i][j]=1;
 }
for(int i=1;i<=n;i++)
 {
  for(int j=1;j<=m;j++)
    if(a[i][j]==0) v[i][j]=v[i-1][j]+1;
    else v[i][j]=0;
  for(int j=1;j<=m;j++)
   {
    if(j==1) {nr=1; stiva[1]=1;}
    else {
          nr++;
          while(v[i][stiva[nr-1]]>v[i][j])
         {
          nr--;
          d[stiva[nr]]=j;
         }
         stiva[nr]=j;
         }
   }
  for(int j=1;j<=nr;j++)
  d[stiva[j]]=m+1;
  for(int j=m;j>=1;j--)
  {
   if(j==m) {nr=1; stiva[1]=m;}
   else {
         nr++;
         while(v[i][stiva[nr-1]]>v[i][j])
         {
          nr--;
          s[stiva[nr]]=j;
         }
         stiva[nr]=j;
        }
  }
  for(int j=1;j<=m;j++)
   if(v[i][j]*(d[j]-s[j]-1)>arie1)
    {
     c1=s[j]+1;
     c2=d[j]-1;
     l1=i-v[i][j]+1;
     l2=i;
     arie1=v[i][j]*(d[j]-s[j]-1);
    }
 }
for(int i=l1;i<=l2;i++)
  for(int j=c1;j<=c2;j++)
 a[i][j]=1;
for(int i=1;i<=n;i++)
 {
  for(int j=1;j<=m;j++)
    if(a[i][j]==0) v[i][j]=v[i-1][j]+1;
    else v[i][j]=0;
  for(int j=1;j<=m;j++)
   {
    if(j==1) {nr=1; stiva[1]=1;}
    else {
          nr++;
          while(v[i][stiva[nr-1]]>v[i][j])
         {
          nr--;
          d[stiva[nr]]=j;
         }
         stiva[nr]=j;
         }
   }
  for(int j=1;j<=nr;j++)
  d[stiva[j]]=m+1;
  for(int j=m;j>=1;j--)
  {
   if(j==m) {nr=1; stiva[1]=m;}
   else {
         nr++;
         while(v[i][stiva[nr-1]]>v[i][j])
         {
          nr--;
          s[stiva[nr]]=j;
         }
         stiva[nr]=j;
        }
  }
  for(int j=1;j<=m;j++)
   if(v[i][j]*(d[j]-s[j]-1)>arie2)
    {
     arie2=v[i][j]*(d[j]-s[j]-1);
    }
 }
g<<arie1+arie2;
}