#include <iostream>
using namespace std;

int main() {
    int a[4],i,j,aux;
    for(i=1;i<=4;i++){
        cin>>a[i];
    }
    for(i=1;i<=4;i++){
        for(j=1;j<=4;j++){
            if(a[i]>a[j]){
                aux = a[i];
                a[i] = a[j];
                a[j] = aux;
            }
        }
    }
    cout<<a[1]*a[2]+a[3]*a[4];
    return 0;
}