import java.util.*

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

  val qp = 4 * q
  val hp = 2 * h
  val qh = Math.min(qp, hp)
  val min = Math.min(qh, s)

  val ans = mutableListOf<Long>()

  val case1 = n * min
  ans.add(case1)
  
  var tmpN = 0L
  if (n % 2L != 0L) {
    tmpN = 1L
  }
  val case2 = n / 2L * d + tmpN * min
  ans.add(case2)

  println(ans.min())
}