/**
  * http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ITP1_10_C&lang=jp
  * Math Functions - Standard Deviation
  */
object Main {
  def main(args: Array[String]): Unit = {
    Iterator.continually(io.StdIn.readLine()).takeWhile(_ != null).map(_.toInt).takeWhile(_ != 0)
      .map {
        n => {
          val scores = io.StdIn.readLine().split(" ").map(_.toDouble)
          val mean = scores.sum / n
          math.sqrt(scores.foldLeft(0.0)((acc, x) => acc + x * x) / n - (mean * mean))
        }
      }
      .foreach(println)
  }
}