#include <cstdio>
#include <algorithm>

using namespace std;

int main() {
    //freopen("data.in", "r", stdin);
    //freopen("data.out", "w", stdout);

    int v[5];

    for ( int i = 1; i <= 4; i++ ) {
        scanf("%d", &v[i]);
    }

    sort(v+1, v+5);

    printf("%d\n", v[1] * v[2] + v[3] * v[4]);
    return 0;
}