#include<bits/stdc++.h>
using namespace std;
long long q,h,s,d,n,ans,cnt;
int main()
{
    cin>>q>>h>>s>>d>>n;
    cnt=min(q*4,min(h*2,s));
    if(cnt*2<=d)
    cout<<cnt*n<<endl;
    else
    cout<<((n%2)*cnt)+n/2*d<<endl;
    return 0;
}