#include <bits/stdc++.h>
#define ll long long

using namespace std;

ll a[10],e,ans,bigOne,bigTwo;

int main(){

	cin>>a[0]>>a[1]>>a[2]>>a[3];
	cin>>e;
	a[0]*=4;
	a[1]*=2;
	bigOne=min(a[0],min(a[1],a[2]));
	bigTwo=min(2*bigOne,a[3]);
	ll tmp = e;
	if(tmp>1){
		ll total = tmp/2;
		ans = total*bigTwo;
		if(tmp%2==1){
			ans+=bigOne;
		}
	}else{
		cout << bigOne<<endl;
		return 0;
	}
	cout << ans<<endl;


	return 0;
}
