import java.util.*

fun main(args: Array<String>) {
    val sc = Scanner(System.`in`)
    val q = sc.nextLong()
    val h = sc.nextLong()
    var s = sc.nextLong()
    val d = sc.nextLong()
    val n = sc.nextLong()

    s = arrayOf(4 * q, 2 * h, s).min()!!
    println(Math.min(2 * s, d) * (n / 2) + s * (n % 2))
}
