
import scala.util.control.Breaks
import Math._
object Main extends App {
  val b = new Breaks
  b.breakable {
    while (true) {
      val n = readLine.toInt

      if (n == 0) b.break()

      val s = readLine.split(' ').map(_.toDouble)

      val m = s.sum / s.length
      val a = s.map(t => (t-m)*(t-m)).sum / s.length
      println(sqrt(a))
    }
  }
}
