#include <iostream>

using namespace std;
int a, b, c, d, x, q, i;
int main()
{
    cin>>a>>b>>c>>d;
    x=a*b+c*d;
    q=a*c+b*d;
    i=a*d+c*b;
    if(x>=q)
        {
            if(x>=i) cout<<x;
             else cout<<i;
        }
    if(x<q)
        {
            if(q>i) cout<<q;
             else cout<<i;
        }
    return 0;
}