#include <fstream>
#include <bitset>
using namespace std;
ifstream fin("bmatrix.in");
ofstream fout("bmatrix.out");
bitset<201>v[201];
int tot[201][201];
int main()
{
    int n,m,i,j,u,z,pas,x,y,x1,x2,x3,y1,y2,y3;
    fin>>n>>m;
    char ok;
    for(i=1;i<=n;i++)
    {
        for(j=1;j<=m;j++)
        {
            fin>>ok;
            v[i][j]=ok-'0';
            tot[i][j]=tot[i][j-1]+tot[i-1][j]-tot[i-1][j-1]+v[i][j];
        }
    }
    int arie1=0,arie2=0;
    for(i=1;i<=n;i++)
    {
        for(j=1;j<=m;j++)
        {
            for(u=i;u<=n;u++)
            {
                for(z=j;z<=m;z++)
                {
                    if(tot[u][z]-tot[i-1][z]-tot[u][j-1]+tot[i-1][j-1]==0)
                    {
                        pas=(u-i+1)*(z-j+1);
                        if(pas>arie1)
                        {
                            arie2=arie1;
                            arie1=pas;
                            x2=x,y2=y,x3=x1,y3=y1;
                            x=i,y=j,x1=u,y1=j;
                        }
                        else
                        {
                            if(pas>arie2)
                            {
                                if(!(i>=x2&&j>=y2&&u<=x3&&z<=y3)) arie2=pas;
                            }
                        }
                    }
                }
            }
        }
    }
    fout<<arie1+arie2;
}