#include <bits/stdc++.h>
using namespace std;
#define int long long int
int32_t main(){
	int q,h,s,d,n;cin>>q>>h>>s>>d>>n;
	h = min(h,2*q);
	s = min(s,2*h);
	d = min(d,2*s);
	cout<<(n/2)*d+(n&1)*s;
}
