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

unsigned long long int v[10];

int main()
{
    int i;
    unsigned long long int val=0;
    for (i=1; i<=4; ++i) std::cin>>v[i];
    sort(v, v+4);
    val=v[1]*v[2];
    val+=v[3]*v[4];
    std::cout<<val;
    return 0;
}