#include <fstream>
using namespace std;
ifstream fin ("bmatrix.in");
ofstream fout ("bmatrix.out");
int n,m,i,j,i1,aria,i2,j1,j2,k,maxc,maxc1,st[205],dr[205],stiva[205],a[205];
bool v[205][205];
char ch;
int main()
{
    fin>>n>>m;
    for (i=1; i<=n; i++)
    {
        for (j=1; j<=m; j++)
        {
            fin>>ch;
            v[i][j]=ch-'0';
        }
    }
    for (i=1; i<=n; i++)
    {
        for (j=1; j<=m; j++)
        {
            if (v[i][j]==0)
                a[j]++;
            else
                a[j]=0;
        }
        k=0;
        for (j=1; j<=m; j++)
        {
            while (k>0&&a[j]<=a[stiva[k]])
                k--;
            if (k>0)
                st[j]=stiva[k]+1;
            else
                st[j]=1;
            k++;
            stiva[k]=j;
        }
        k=0;
        for (j=m; j>0; j--)
        {
            while (k>0&&a[j]<=a[stiva[k]])
                k--;
            if (k>0)
                dr[j]=stiva[k]-1;
            else
                dr[j]=m;
            k++;
            stiva[k]=j;
        }
        for (j=1; j<=m; j++)
        {
            aria=(dr[j]-st[j]+1)*a[j];
            if (aria>maxc)
            {
                maxc=aria;
                j1=st[j];
                j2=dr[j];
                i2=i;
                i1=i2-a[j]+1;
            }
        }
    }
    for (i=i1; i<=i2; i++)
    {
        for (j=j1; j<=j2; j++)
            v[i][j]=1;
    }
    for (j=1; j<=m; j++)
        a[j]=0;
    for (i=1; i<=n; i++)
    {
        for (j=1; j<=m; j++)
        {
            if (v[i][j]==0)
                a[j]++;
            else
                a[j]=0;
        }
        k=0;
        for (j=1; j<=m; j++)
        {
            while (k>0&&a[j]<=a[stiva[k]])
                k--;
            if (k>0)
                st[j]=stiva[k]+1;
            else
                st[j]=1;
            k++;
            stiva[k]=j;
        }
        k=0;
        for (j=m; j>0; j--)
        {
            while (k>0&&a[j]<=a[stiva[k]])
                k--;
            if (k>0)
                dr[j]=stiva[k]-1;
            else
                dr[j]=m;
            k++;
            stiva[k]=j;
        }
        for (j=1; j<=m; j++)
        {
            aria=(dr[j]-st[j]+1)*a[j];
            if (aria>maxc1)
                maxc1=aria;
        }
    }
    fout<<maxc+maxc1;
    return 0;
}