void main()
{
    long[] tmp = readln.split.to!(long[]);
    long q = tmp[0], h = tmp[1], s = tmp[2], d = tmp[3];
    long n = readln.chomp.to!long;

    long div = n / 2, rem = n % 2;
    long l = min(4 * q, 2 * h, s);

    writeln(min(2 * l, d) * div + l * rem);
}

import std.stdio;
import std.string;
import std.array;
import std.conv;
import std.algorithm;
import std.range;
import std.math;
import std.numeric;
import std.container;
import std.typecons;
import std.ascii;
import std.uni;