#include <bits/stdc++.h>
using namespace std;
int main()
{
	unsigned long long a,b,c,d,n,mn;
	cin>>a>>b>>c>>d>>n;
	b=min(b,2*a);
	c=min(c,2*b);
	d=min(d,2*c);
	mn=d*(n/2)+c*(n%2);
	cout<<mn<<endl;
	return 0;}