#include<stdio.h>
#include<iostream>
using namespace std;
typedef long long int ll;
ll a[5],n;
int main()
{
	cin>>a[0]>>a[1]>>a[2]>>a[3];
	cin>>n;
	for(int i=1;i<=4;i++)
		a[i]=min(a[i],2*a[i-1]);
	printf("%lld\n",n/2*a[3]+(n&1)*a[2]);
	return 0;
}