#include<iostream>
#include<algorithm>
using namespace std;
int a,b,c,d,v[5];
int main()
{
    cin>>a>>b>>c>>d;
    v[1]=a;v[2]=b;v[3]=c;v[4]=d;
    sort(v,v+1,4);
    cout<<v[4]*v[3]+v[1]*v[2];
    return 0;
}