import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

int readint() {
    return readln.chomp.to!int;
}

int[] readints() {
    return readln.split.map!(to!int).array;
}

void main() {
    auto xs = readints;
    long q = xs[0];
    long h = xs[1];
    long s = xs[2];
    long d = xs[3];
    long one = min(q * 4, h * 2, s);
    long two = min(one * 2, d);

    auto n = readint;
    long ans = (n / 2) * two + (n % 2) * one;
    writeln(ans);
}
