#include <bits/stdc++.h>
using namespace std;
int main () {
  long Q, H, S, D, N;
  cin >> Q >> H >> S >> D >> N;
  S = min(S, min(Q * 4, H * 2));
  D = min(D, S * 2);
  cout << (N % 2 == 0? N * D / 2: S + (N / 2) * D) << endl;
  return 0;
}