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