import java.util.*

fun main(args: Array<String>) {
    val pw = java.io.PrintWriter(System.out)
    Problem.solve(Scanner(System.`in`), pw)
    pw.flush()
}

fun <A : Comparable<A>> min(a: A, b: A) = if (a < b) a else b
fun <A : Comparable<A>> minOf(vararg a: A) = a.reduce { acc, x -> min(acc, x) }

object Problem {
    fun solve(sc: Scanner, pw: java.io.PrintWriter) {
        val Q = sc.next().toLong()
        val H = sc.next().toLong()
        val S = sc.next().toLong()
        val D = sc.next().toLong()
        val N = sc.next().toLong()
        val q1 = minOf(4 * Q, 2 * H, S)
        val q2 = minOf(2 * q1, D)
        pw.println((N / 2) * q2 + (N % 2) * q1)
    }
}
