#include <cstdio>
#include <algorithm>
#include <vector>

using namespace std;
vector <int>v;
int main(){
int a;
scanf("%d",&a);
v.push_back(a);
scanf("%d",&a);
v.push_back(a);
scanf("%d",&a);
v.push_back(a);
scanf("%d",&a);
v.push_back(a);

sort(v.begin(),v.end());
printf("%d",v[0]*v[1]+v[2]*v[3]);

return 0;
}