#include<iostream>

using namespace std;

int main()
{
	float v[4], aux;
	int i, j;
	cin>>v[1]>>v[2]>>v[3]>>v[4];
	for(i=1;i<=4;i++)
		for(j=1;j<=4;j++)
			if(v[j]<v[i])
			{
				aux=v[j];
				v[j]=v[i];
				v[i]=aux;
			}
	cout<<v[1]*v[2] + v[3]*v[4];
	return 0;
}