#include <cstdio>
#include <algorithm>
using namespace std;
int v[7];
int main()
{
    scanf("%d",&v[1]);
    scanf("%d",&v[2]);
    scanf("%d",&v[3]);
    scanf("%d",&v[4]);
    sort(v+1,v+5);
    printf("%d\n",v[4]*v[3]+v[2]*v[1]);
    return 0;
}