#include<stdio.h>
#include<algorithm>
using namespace std;
int v[10];
int main()
{
    scanf("%ld %ld %ld %ld",&v[1],&v[2],&v[3],&v[4]);
    sort(v+1,v+1+4);
    printf("%ld",v[1]*v[2]+v[3]*v[4]);
}