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