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

vector < int > a;
int i, x;
int main()
{
    for(i = 1; i <= 4; i++)
    {
        cin >> x;
        a.push_back(x);
    }

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