object Main {
  def main(args: Array[String]) {
    val input = io.Source.stdin.getLines().mkString("\n");
    println(solve(input))

    def solve(input: String): String = {
      val _ :: s :: _ = input.split("\n").toList
      val ls = s.split(" ").map(_.toDouble).sorted
      val first :: second :: left = ls.toList
      left
        .foldLeft((first + second) / 2) { (acc, i) =>
          (acc + i) / 2
        }
        .toString
    }
  }
}