#include<fstream>
using namespace std;

int a,b,c,d,max1;
int main()
{
    ifstream f("Input");
    ofstream g("Output");
    f>>a>>b>>c>>d;

    max1 = a*b+c*d;
    if (a*c+b*d>max1)
        max1=a*c+b*d;

    if (a*d + c*b > max1)
        max1 = a*d + c*b;

    g<<max1<<"\n";

    return 0;
}