#include <bits/stdc++.h>
using namespace std;



int main() {

	long long a , b , c , d , n;
	cin >> a >> b >> c >> d >> n;
	b = min(b , a<<1);
	c = min(c , b<<1);
	d = min(d , c<<1);

	cout << (n/2) * d + (n%2) * c << endl;

	return 0;
}
