#include <iostream>

using namespace std;

int a, b, c, d;

int main()
{
cin>>a>>b>>c>>d;

int x1=a*b+c*d;
int x2=a*c+b*d;
int x3=a*d+b*c;
if(x1>x2)
    x2=x1;
if(x2>x3)
    x3=x2;

cout<<x3;


    return 0;
}