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

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

int main() {
    cin >> q >> h >> s >> d >> n;
    cout << n / 2 * min({d, s * 2, h * 4, q * 8}) + n % 2 * min({s, h * 2, q * 4}) << endl;
    return 0;
}