import scala.io.StdIn
import Math.{sqrt,pow}
/**
  * AOJ
  */
object Main {

  def main(args: Array[String]): Unit = {
    while(true){
      val n = StdIn.readInt()
      if(n == 0){return}
      val sArray = StdIn.readLine().split(" ").map(_.toDouble)
      val m:Double = sArray.sum / n
      println("%.8f".format(sqrt(sArray.foldLeft(0.toDouble){(x,y) => x + pow(y - m,2)} / n)))
    }
  }
}