#include <fstream>
using namespace std;
ifstream fin("bmatrix.in");
ofstream fout("bmatrix.out");
bool mat[1001][1001];
char ch;
int jos[1001][1001], stanga[1001][1001], n, m, i, j, Max1, Max2;
int main() {
    fin >> n >> m;
    for ( i = 1; i <= n; i++ )
        for ( j = 1; j <= m; j++ ) {
            fin >> ch;
            mat[i][j] = ch - '0';
            if ( !mat[i][j] ) {
                stanga[i][j] = stanga[i][j-1] + 1;
                jos[i][j] = jos[i-1][j] * ( stanga[i][j] == stanga[i-1][j] ) + 1;
            }
        }
    for ( i = 1; i <= n; i++ )
        for ( j = 1; j <= m; j++ )
            if ( !mat[i][j] && ( i == n || mat[i+1][j] ) && ( j == m || mat[i][j+1] ) )
                if ( Max1 <= stanga[i][j] * jos[i][j] ) {
                    Max2 = max(Max2, Max1);
                    Max1 = stanga[i][j] * jos[i][j];
                } else if ( Max2 <= stanga[i][j] * jos[i][j] )
                    Max2 = stanga[i][j] * jos[i][j];
    fout << Max1 + Max2;
    return 0;
}