import scala.io.StdIn.{readLine,readDouble}

object Main extends App {

  def read():Unit = {
    val n = readDouble
    if(n!=0) {
      val line = readLine.split(" ").map(_.toDouble)
      val avg = line.sum / n

      println(Math.sqrt(line.foldLeft(0d)( (x,y) => x + (y - avg)*(y - avg) )/n))
      read()
    }
  }

  read()
}