#include<iostream>
#include<algorithm>


using namespace std;

int v[5];



int main()
{

    int a , b , c , d;
    cin >> a >> b >> c >> d;

    v[1] = a;
    v[2] = b;
    v[3] = c;
    v[4] = d;
    sort(v+1,v+5);
    cout <<v[1] * v[2] + v[3]*v[4];
    return 0;

}