#include <fstream>
#include<algorithm>
using namespace std;
ifstream in("input.in");
ofstream out("output.out");
int main()
{int v[5];
in>>v[1]>>v[2]>>v[3]>>v[4];
sort(v+1,v+4+1);
out<<v[1]*v[2]+v[3]*v[4];
}