#include <fstream>
using namespace std;
ifstream f("bmatrix.in");
#define LE 216
ofstream g("bmatrix.out");
int n,m,i,j,high[LE][LE],Area[LE][LE],a[LE][LE],a2[LE][LE];
int lat,result;
int Adr[LE],Ast[LE];
string sir;
#define inf 1<<30
int main()
{
    f>>n>>m;


    for(i=1; i<=n; ++i)
    {
        f>>sir;
        for(j=0; j<m; ++j)
            a[i][j+1]=1-(sir[j]-'0');
    }

    for(i=1; i<=n; ++i)
        for(j=1; j<=m; ++j)
        {
            if (a[i][j]==0) high[i][j]=0;
            else high[i][j]=1+high[i-1][j];
        }


    for(i=1; i<=n; ++i)
        for(j=1; j<=m; ++j)
        {
            lat=inf;
            for(int side=j; side>=1&&high[i][side]!=false; side--)
            {
                lat=min(lat,high[i][side]);
                Area[side][j]=max(Area[side][j],lat*(j-side+1));
            }
        }

    for(i=1; i<=m; ++i)
    {
        Ast[i]=max(Ast[i],Ast[i-1]);
        for(j=1; j<=i; ++j)
            Ast[i]=max(Area[j][i],Ast[i]);
    }

    for(i=m; i>=1; i--)
    {
        Adr[i]=max(Adr[i],Adr[i+1]);
        for(j=i; j<=m; j++)
            Adr[i]=max(Adr[i],Area[i][j]);
    }

    for(i=1; i<=m; ++i)
        for(j=i+1; j<=m; ++j)
            result=max(result,Ast[i]+Adr[j]);


    /*   for(i=1; i<=n; ++i)
           for(j=1; j<=m; ++j)
               a2[j][i]=a[i][j];
       swap(n,m);
       for(i=1; i<=n; ++i)
           for(j=1; j<=m; ++j)
               a[i][j]=a2[i][j];
    */
    g<<result<<'\n';


    f.close();
    g.close();
    return 0;
}