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

long long Q, H, S, D, N;

int main() {
    cin >> Q >> H >> S >> D >> N;
    cout << (N / 2) * min({8 * Q, 4 * H, 2 * S, D}) + (N % 2) * min({4 * Q, 2 * H, S}) << "\n";
}
