#include <fstream>
#include <vector>
#include <cstring>
using namespace std;
ifstream fin("bmatrix.in");
ofstream fout("bmatrix.out");

bool v[205][205];
int r[205][205];

int n,m;

int largest_rect(bool v[205][205],int sn,int sm,int n,int m)
{

    int maximum = 0;
    memset(r,0,sizeof(r));
    for(int i=sn; i<=n; i++)
    {
        vector <int> stk;
        for(int j=sm; j<=m+1; j++)
        {
            if(v[i][j])
                r[i][j]=0;
            else
                r[i][j]=r[i-1][j]+1;
            if(j==m+1)
                r[i][j]=0;
            while(!stk.empty() && r[i][j]<=r[i][stk.back()])
            {
                int h = r[i][stk.back()];
                stk.pop_back();
                int w = j-1;
                if(!stk.empty())
                    w-=stk.back();
                else
                    w=w-sm+1;
                if(maximum < h*w)
                    maximum=h*w;
            }
            stk.push_back(j);
        }
    }
    return maximum;
}


int main()
{
    fin>>n>>m;
    for(int i=1; i<=n; i++)
    {
        char ch;
        for(int j=1; j<=m; j++)
            fin>>ch,v[i][j]=ch-'0';
    }
    int mxsol = 0;
    for(int i=1;i<m;i++)
    {
        int s1 = largest_rect(v,1,1,n,i);
        int s2 = largest_rect(v,1,i+1,n,m);
        mxsol=max(mxsol,s1+s2);
    }
    for(int i=1;i<n;i++)
    {
        int s1 = largest_rect(v,1,1,i,m);
        int s2 = largest_rect(v,i+1,1,n,m);
        mxsol=max(mxsol,s1+s2);
    }
    fout<<mxsol;

}