#include<iostream>
//#include<algorithm>
using namespace std;
int main()
{
	int a,b,c,d,x,y,z;
cin>>a>>b>>c>>d;
x=a*b+c*d;
y=a*c+b*d;
z=a*d+b*c;
cout<<max(max(x,y),z);

return 0;
}