#include <iostream>
#include <algorithm>
using namespace std;
int v[4];
int main()
{
    cin>>v[1]>>v[2]>>v[3]>>v[4];
    sort(v+1,v+4+1);
    cout<<max(v[1]*v[2]+v[3]*v[4],v[1]*v[4]+v[2]*v[3]);
    return 0;
}