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