#include <iostream>
#include <algorithm>
#include <queue>
#include <set>
#include <map>
#include <string>
using namespace std;

int a[4];

int main() {
    cin >> a[0] >> a[1] >> a[2] >> a[3];
    sort (a, a + 4);
    cout << a[0] * a[1] + a[2] * a[3];
    return 0;
}