#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    ifstream f("input.in");
    ofstream g("output.out");
    unsigned a,b,c,d,x;
    f>>a>>b>>c>>d;
    f.close();
    x=a*b+c*d;
    if(a*c+b*d>x)
        x=a*c+b*d;
    if(a*d+b*c>x)
        x=a*d+b*c;
    g<<x;
    g.close();
    return 0;
}