object Main {
  def main(args: Array[String]): Unit = {
    val scanner = new java.util.Scanner(System.in)

    while(true) {
      val n = scanner.nextInt
      if(n == 0) System.exit(0)
      val ns = Seq.fill(n)(scanner.nextInt)

      val m = ns.sum.toDouble / n
      println(f"${math.sqrt(ns.foldLeft(0.0d){ case (s, si) => s + (si - m) * (si - m) } / n)}%.5f")
    }
  }
}

