while n= gets.to_i
    break if n == 0
    points = gets.split.map(&:to_f)
    sum = 0
    # puts points.join(" ")
     #???sum????¨????
    points.each{|point| sum += point}
    m = sum/(n)
    #puts sum
    #puts average
    var = 0.0
    points.each{|pt| var  +=  (pt - m)**2}
    #puts array.join(" ")
    puts Math.sqrt(var/n)
end