#include <iostream>
#include <cstring>
#include <algorithm>
#include <cstdio>
#include <fstream>
#define MAX 256

using namespace std;

int n, m, sol;
int ars[MAX];
int mas[MAX][MAX], maj[MAX][MAX];
char mac[MAX][MAX];

void calc()
{
    memset(ars,0,sizeof(ars));
    memset(maj,0,sizeof(maj));
    memset(mas,0,sizeof(mas));
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
            if (mac[i][j]=='0')
                mas[i][j]=mas[i-1][j]+1;
            else mas[i][j]=0;
        int el=n+1-i;
        for(int j=1;j<=m;j++)
            if (mac[el][j]=='0')
                maj[el][j]=maj[n+2-i][j] + 1;
            else maj[el][j]=0;
    }
    for(int i=1;i<=n;i++)
    {
        ars[i]=ars[i-1];
        for(int stj=1;stj<=m;stj++)
        {
            int mings=MAX;
            for(int fnj=stj;fnj<=m;fnj++)
            {
                mings=min(mings,mas[i][fnj]);
                ars[i]=max(ars[i],mings*(fnj-stj+1));
            }
        }
    }
    for(int i=n;i;i--)
        for(int stj=1;stj<=m;stj++)
        {
            int mings=MAX;
            for(int fnj=stj;fnj<=m;fnj++)
            {
                mings=min(mings,maj[i][fnj]);
                sol=max(sol,ars[i-1]+mings*(fnj-stj+1));
            }
        }
}
int main()
{
    ifstream cin("bmatrix.in");
    ofstream cout("bmatrix.out");
    cin>>n>>m;
    for(int i=1;i<=n;i++)
        fgets(mac[i]+1,MAX,stdin);
    calc();
    for(int i=1;i<=max(n,m);i++)
        for(int j=i+1;j<=max(n,m);j++)
            swap(mac[i][j],mac[j][i]);
    swap(n,m);
    calc();
    cout<<sol<<"\n";
    return 0;
}