#include <fstream>
#include <stack>
#include <string>

using namespace std;

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

const int nmax= 200;

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

stack <int> s;

void rotate(  ) {
    int aux[nmax+1][nmax+1];
    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 i= x1; i<=x2; ++i ) {
        for ( int j= 1; j<=m; ++j ) {
            if ( i==x1 ) a[j]= 0;

            if ( v[i][j]==0 ) ++a[j];
            else a[j]= 0;
        }

        for ( ; !s.empty(); s.pop() ) ;
        for ( int j= 1; j<=m; ++j ) {
            for ( ; !s.empty() && a[j]<=a[s.top()]; s.pop() ) ;
            if ( s.empty() ) x[j]= 1;
            else x[j]= s.top()+1;

            s.push(j);
        }
        for ( ; !s.empty(); s.pop() ) ;
        for ( int j= m; j>=1; --j ) {
            for ( ; !s.empty() && a[j]<=a[s.top()]; s.pop() ) ;
            if ( s.empty() ) y[j]= m;
            else y[j]= s.top()-1;

            s.push(j);
            ans= max(ans, a[j]*(y[j]-x[j]+1));
        }
    }

    return ans;
}

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

    return ans;
}

int main(  ) {
    fin>>n>>m;
    for ( int i= 1; i<=n; ++i ) {
        string s;
        fin>>s;
        for ( int j= 1; j<=m; ++j ) {
            v[i][j]= s[j-1]-'0';
        }
    }

    int sol1= solve(), sol2, sol;
    rotate();
    sol2= solve();
    sol= max(sol1, sol2);

    fout<<sol<<"\n";

    return 0;
}