#include <iostream>
using namespace std;
int v[6],aux,ok,s;
int main()
{
    for(int i=1;i<=4;i++)
        cin>>v[i];
        ok=1;
    while(ok==1){
        ok=0;
        for(int i=1;i<4;i++){
            if(v[i]>v[i+1]){
                ok=1;
                aux=v[i];
                v[i]=v[i+1];
                v[i+1]=aux;
            }
        }
    }
    s=v[4]*v[3]+v[2]*v[1];
    cout<<s;
    return 0;
}