#include<bits/stdc++.h>
using namespace std;
#define debug(...)   printf( __VA_ARGS__ )
//#define debug(...)   /****nothing****/
#define pb push_back
#define mp make_pair
#define LL long long
#define resett(arr,val,N) for(int ii=0;ii<(N);ii++) arr[ii]=val;
const int MX=1e6;
LL n,a,b,c,d,x,y,ar[MX];

int main()
{
    //freopen("d://i.txt","r",stdin);
    //freopen("d://o.txt","w",stdout);
    ios::sync_with_stdio(false), cin.tie(0), cout.tie(0) ;
    while(cin>>a>>b>>c>>d>>n)
    {
        b=min(2*a,b);
        c=min(2*b,c);
        if(c*2<=d)
            cout<<1LL*n*c<<endl;
        else
            cout<<(1LL*(n/2)*d + 1LL*(n%2)*c)<<endl;

    }

    return 0;
}


