#include <bits/stdc++.h>

using namespace std;

ifstream fin("bmatrix.in");
ofstream fout("bmatrix.out");

int n,m;
int a[205][205],r[205][205],smen[205][205];

int main()
{
    fin>>n>>m;
    for(int i=1; i<=n; i++)
    {
        for(int j=1; j<=m; j++)
        {
            char ch;
            fin>>ch;
            a[i][j]=ch-'0';
        }
    }
    for(int i=1; i<=n; i++)
    {
        for(int j=m; j>=1; j--)
        {
            if(a[i][j]==0)
                r[i][j]=r[i][j+1]+1;
        }
    }
    int m1=0,m2=0;
    for(int i=1; i<=n; i++)
    {
        for(int j=1; j<=m; j++)
        {
            smen[i][j]+=smen[i][j-1]+smen[i-1][j]-smen[i-1][j-1];
            if(a[i][j]==1 || smen[i][j]>0)
                continue;
            int minim=m+1,maxim=0,down;
            for(int k=i; k<=n && a[k][j]==0; k++)
            {
                minim=min(minim,r[k][j]);
                if(maxim<minim*(k-i+1))
                {
                    maxim=minim*(k-i+1);
                    down=k;
                }
            }
            smen[i][j]++;
            smen[down+1][j]--;
            smen[i][j+maxim/(down-i+1)]--;
            smen[down+1][j+maxim/(down-i+1)]++;
            if(maxim>=m1)
            {
                m2=m1;
                m1=maxim;
            }
            else if(maxim>m2)
                m2=maxim;
        }
    }
    fout<<m1+m2<<"\n";
    return 0;
}