#include <iostream>

using namespace std;

int main()
{
    short a,b,c,d;
    int s;
    cin>>a>>b>>c>>d;
    s=a*b+c*d;
    if(a*c+b*d>s)
    s=a*c+b*d;
    if(a*d+b*c>s)
    s=a*d+b*c;
    cout<<s;
    return 0;
}