#include <bits/stdc++.h>

using namespace std;
ifstream in("bmatrix.in");
ofstream out("bmatrix.out");
const int NMAX = 201;

int a[NMAX][NMAX];
int lin_sus[NMAX], lin_jos[NMAX];
int n, m;
void debug(){
    for( int l = 1; l <= n; l++ ){
        for( int c = 1; c <= m; c++ )
            out << a[l][c];
        out << "\n";
    }
    out << "\n";
}
int skyline( deque <int> dq ){
    int x = dq.size(), aria = 0;
    for( int i = 0; i < x; i++ )
        aria = max( aria, dq.front() * (x-i) ), dq.pop_front();
    return aria;
}
void bmatrix( int linie_sus[NMAX], int tip ){
    int up[NMAX];
    for( int i = 1; i <= m; i++ )
        up[i] = 0;
    for( int l = 1; l <= n; l++ ){
        int aria = 0;
        deque <int> dq;
        for( int c = 1; c <= m; c++ ){
            if( !a[l][c] ){
                if( tip )
                    up[c]++;
                aria = max( aria, up[c] );
                int lenght = 1;
                while( dq.size() && up[c] < dq.back() ){
                    dq.pop_back();
                    lenght++;
                }
                aria = max( aria, lenght * up[c]);
                dq.push_back(up[c]);
                aria = max( aria, skyline(dq) );
                if( !tip )
                    up[c]++;
            }
            else{
                up[c] = 0;
                dq.clear();
            }
        }
        linie_sus[l] = aria;
    }
}
int main()
{
    in >> n >> m;
    for( int l = 1; l <= n; l++ ){
        char ch;
//        in >> ch;
        for( int c = 1; c <= m; c++ ){
            in >> ch;
            a[l][c] = ch - '0';
        }
    }
//    debug();
    bmatrix(lin_sus, 1);
    for( int l = 1; l <= n/2; l++ )
        for( int c = 1; c <= m; c++ ){
            int aux = a[l][c];
            a[l][c] = a[n-l+1][c];
            a[n-l+1][c] = aux;
        }
    bmatrix(lin_jos, 0);
//    debug();
    int rez = 0;
    for( int i = 1; i <= n; i++ ){
        rez = max( rez, lin_sus[i] + lin_jos[n-i+1] );
//        out << lin_sus[i] << " " << lin_jos[n-i+1] << "\n";
    }
    out << rez;
    return 0;
}