#include <iostream>
#include <algorithm>
#include <vector>

using namespace std ;
int  v[5];
vector <int> Q ;
int sum ;
int main()
{
for(int i = 1 ; i <= 4; ++ i)
{cin >> v[i] ;
Q.push_back(v[i]) ;
}
sort(Q.begin() , Q.end());
cout << Q[0] * Q[1] + Q[2] * Q[3] ;

return 0;
}