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