#include <iostream>

using namespace std;

int main()
{
   int m1,m2,m3,m4;
    for(int i=1;i<=4;i++){
        int n;
        cin >> n;
        if(n>m1){
            m4=m3;
            m3=m2;
            m2=m1;
            m1=n;
        }else if (n>m2){
             m4=m3;
            m3=m2;
            m2=n;
        }else if (n>m3){
             m4=m3;
            m3=n;

        }else m4=n;
    }
    cout<<m1*m2+m3*m4;
}