object Main extends App {
    val in = io.Source.stdin.getLines.map(_.split(" ").map(_.toInt))
    while (in.next.head != 0) {
        var m = 0.0
        var mean = 0.0
        var n = 0
        for (d <- in.next) {
            m += (d - (d + n * mean) / (n + 1)) * (d - mean)
            mean += (d - mean) / (n + 1)
            n += 1
        }
        println(math.sqrt(m / n))
    }
}