#include <iostream>

using namespace std;

int main()
{
    int a,b,c,d,e;
    cin>>a>>b>>c>>d;
    if(a<=0||a>=100||b<=0||b>=100||c<=0||c>=100||d<=0||d>=100) return 0;
    if(a<b){
        e=a;
        a=b;
        b=e;
    }
    if(a<c){
        e=a;
        a=c;
        c=e;
    }
    if(a<d){
        e=a;
        a=d;
        d=e;
    }
    if(b<c){
        e=b;
        b=c;
        c=e;
    }
    if(b<d){
        e=b;
        b=d;
        d=e;
    }
    cout<<a*b+c*d;
    return 0;
}