#include <cstdio>
#include <algorithm>

using namespace std;

int v[4];

int main() {
    scanf( "%d%d%d%d", &v[0], &v[1], &v[2], &v[3] );
    sort( v, v + 4 );

    int s = v[0] * v[1] + v[2] * v[3];
    printf( "%d\n", s );
}