object Main extends App {
  val sc = new java.util.Scanner(System.in)
  val Q, H, S, D, N = sc.nextLong()
  val oneLiterPrice = Seq(4 * Q, 2 * H, S).min
  val twoLiterPrice = (oneLiterPrice * 2) min D
  println((N / 2) * twoLiterPrice + (N % 2) * oneLiterPrice)
}
