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(_.toInt)
      val m:Double = sArray.sum / n
      println(sqrt(sArray.map(x => pow((x - m),2)).sum / n))
    }
  }
}