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

int main()
{
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    vector<int> v;
    v.push_back(a);
    v.push_back(b);
    v.push_back(c);
    v.push_back(d);

    sort(v.begin(), v.end());
    cout << (v[3]*v[2])+(v[1]*v[0]);

    return 0;
}