#include <iostream>
#include <algorithm>

using namespace std;

long long q,h,s,d,n;

int main() {
    cin >> q >> h >> s >> d >> n;
    s = min(s, 4 * q);
    s = min(s, 2 * h);
    d = min(d, 2 * s);
    cout << (n / 2) * d + (n % 2) * s << '\n';
}
