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

int main()
{
    int v[4],a=0;
    cin>>v[1]>>v[2]>>v[3]>>v[4];
    sort(v+1,v+5);
    a=v[1]*v[2]+v[3]*v[4];
    cout<<a;
    return 0;
}