#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 2500;
int mat[MAX_N + 2][MAX_N + 2], up[MAX_N + 2][MAX_N + 2], down[MAX_N + 2][MAX_N + 2], hup[MAX_N + 2], hdown[MAX_N + 2], maxHeight[MAX_N + 2];
int main() {
int n, m;
cin >> n >> m;
for ( int l = 1; l <= n; l++ ) {
for ( int c = 1; c <= m; c++ ) {
char ch;
cin >> ch;
mat[l][c] = ch - '0';
}
}
for ( int l = 1; l <= n; l++ ) {
for ( int c = 1; c <= m; c++ )
up[l][c] = (mat[l][c] ? up[l - 1][c] + 1 : 0);
}
for ( int l = n; l >= 1; l-- ) {
for ( int c = 1; c <= m; c++ )
down[l][c] = (mat[l][c] ? down[l + 1][c] + 1 : 0);
}
int maxWidth = m;
for ( int i = 0; i <= m; i++ )
maxHeight[i] = n;
for ( int l = 1; l <= n; l++ ) {
int cons1 = 0, hup = n, hdown = n;
for ( int c = 1; c <= m; c++ ) {
if ( mat[l][c] ) {
cons1++;
hup = min( hup, up[l][c] );
hdown = min( hdown, down[l][c] );
maxHeight[cons1] = min( maxHeight[cons1], hup + hdown - 1 );
maxHeight[1] = min( maxHeight[1], up[l][c] + down[l][c] - 1 );
} else {
if ( cons1 > 0 )
maxWidth = min( maxWidth, cons1 );
cons1 = 0, hup = n, hdown = n;
}
}
if ( cons1 > 0 )
maxWidth = min( maxWidth, cons1 );
}
for ( int l = 1; l <= n; l++ ) {
int cons1 = 0, hup = n, hdown = n;
for ( int c = m; c >= 1; c-- ) {
if ( mat[l][c] ) {
cons1++;
hup = min( hup, up[l][c] );
hdown = min( hdown, down[l][c] );
maxHeight[cons1] = min( maxHeight[cons1], hup + hdown - 1 );
} else
cons1 = 0, hup = n, hdown = n;
}
}
int maxArea = 0;
for ( int i = 1; i <= maxWidth; i++ ) {
maxHeight[i] = min( maxHeight[i], maxHeight[i - 1] );
maxArea = max( maxArea, maxHeight[i] * i );
}
cout << maxArea;
return 0;
}
