#include <fstream>

using namespace std;

ifstream fin("bmatrix.in");
ofstream fout("bmatrix.out");

const int nmax= 200;

int n, m, sol;
int x[nmax+1], y[nmax+1], a[nmax+1];
int st[nmax+1];

char v[nmax+1][nmax+1], aux[nmax+1][nmax+1];

void rotate(  ) {
    for ( int i= 1; i<=n; ++i ) {
        for ( int j= 1; j<=m; ++j ) {
            aux[j][n-i+1]= v[i][j];
        }
    }

    n= n^m; m= n^m; n= n^m;
    for ( int i= 1; i<=n; ++i ) {
        for ( int j= 1; j<=m; ++j ) {
            v[i][j]= aux[i][j];
        }
    }
}

int maxarea( int x1, int x2 ) {
    int ans= 0;
    for ( int j= 1; j<=m; ++j ) a[j]= 0;
    for ( int i= x1, cnt; i<=x2; ++i ) {
        cnt= 0; st[0]= 0;
        for ( int j= 1; j<=m; ++j ) {
            a[j]= (1-(v[i][j]-'0'))*(a[j]+1);

            for ( ; cnt>=1 && a[j]<=a[st[cnt]]; --cnt ) ;
            x[j]= st[cnt]+1;
            st[++cnt]= j;
        }

        cnt= 0; st[0]= m+1;
        for ( int j= m; j>=1; --j ) {
            for ( ; cnt>=1 && a[j]<=a[st[cnt]]; --cnt ) ;
            y[j]= st[cnt]-1;
            st[++cnt]= j;
            ans= max(ans, a[j]*(y[j]-x[j]+1));
        }
    }

    return ans;
}

void solve(  ) {
    int aux= 0;
    for ( int k= 2; k<=n; ++k ) {
        int max1= maxarea(1, k-1), max2= maxarea(k, n);
        if ( max1*max2!=0 && aux<max1+max2 ) {
            aux= max1+max2;
        }
    }

    sol= max(sol, aux);
}

int main(  ) {
    fin>>n>>m;
    for ( int i= 1; i<=n; ++i ) {
        fin>>v[i]+1;
    }

    solve();
    rotate();
    solve();

    fout<<sol<<"\n";

    return 0;
}