// tested by Hightail - https://github.com/dj3500/hightail
import std.stdio, std.string, std.conv, std.algorithm;
import std.range, std.array, std.math, std.typecons, std.container, core.bitop;

immutable mod = 10^^9 + 7;
immutable inf = 10^^9 + 7;

void main() {
    int q, h, s, d;
    int n;

    scan(q, h, s, d);
    scan(n);

    auto a = new int[](3);
    a[0] = 4 * q;
    a[1] = 2 * h;
    a[2] = s;

    a.sort();

    long ans;

    if (a[0] * 2 < d) {
        ans = 1L * a[0] * n;
    }
    else {
        if (n & 1) {
            ans = a[0] + 1L * d * (n / 2);
        }
        else {
            ans = 1L * d * (n / 2);
        }
    }

    writeln(ans);
}



void scan(T...)(ref T args) {
    string[] line = readln.split;
    foreach (ref arg; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront();
    }
    assert(line.empty);
}



void fillAll(R, T)(ref R arr, T value) {
    static if (is(typeof(arr[] = value))) {
        arr[] = value;
    }
    else {
        foreach (ref e; arr) {
            fillAll(e, value);
        }
    }
} 