#include <fstream>
using namespace std;
ifstream f("input");
ofstream g("output");
long a,b,c,d,aux;
int main()
{
	f>>a>>b>>c>>d;
	if (d>c)
	{
		aux=c;
		c=d;
		d=aux;
	}
	if (c>b)
	{
		aux=b;
		b=c;
		c=aux;
	}
	if (b>a)
	{
		aux=a;
		a=b;
		b=aux;
	}
	if (d>c)
	{
		aux=c;
		c=d;
		d=aux;
	}
	if (c>b)
	{
		aux=b;
		b=c;
		c=aux;
	}
	if (d>c)
	{
		aux=c;
		c=d;
		d=aux;
	}
	g<<a*b+c*d;
	f.close();
	g.close();
	return 0;
}