object Main {
  def main(args: Array[String]): Unit = {
    Iterator.continually(io.StdIn.readLine().toInt)
      .takeWhile(_ != 0)
      .foreach { n =>
        val sn = io.StdIn.readLine().split(" ").map(_.toInt)
        val m = sn.sum / n.toDouble
        val a2 = sn.map { s =>
          val v = s - m
          v * v
        }.sum / n
        println(f"${Math.sqrt(a2)}%.8f")
      }
  }
}