object Main {
    def main(args: Array[String]) = {
        val in = io.Source.stdin.getLines.map(_.split(" ").map(_.toDouble))
        for (n <- in if n(0) != 0) {
            val a = in.next
            println(math.sqrt(a.map(_ - a.sum / a.size).map(b => b * b).sum / a.size))
        }
    }
}