#include<iostream>
#include<queue>
using namespace std;

int a, b, c, d;
priority_queue<int> coada;

int main() {
    cin >> a >> b >> c >> d;
    coada.push(a);
    coada.push(b);
    coada.push(c);
    coada.push(d);
    a = coada.top();
    coada.pop();
    b = coada.top();
    coada.pop();
    c = coada.top();
    coada.pop();
    d = coada.top();
    coada.pop();
    cout << a * b + c * d;
    return 0;
}