#include<iostream>
using namespace std;
int main()
{
	int a,b,c,d,p1,p2;
	cin>>a>>b>>c>>d;
	p1=a*b+c*d;
	p2=a*c+b*d;
	if(p1>p2)
	cout<<p1<<endl;
	else 
	cout<<p2<<endl;
	return 0;
}