while true
  n = gets.to_f
  exit if n == 0
  s = gets.chomp.split(" ").map{|x|x.to_f}
  sum = 0.0
  s.size.times do |i|
    sum += s[i]
  end
  heikin = sum / n
  ans = 0.0
  s.size.times do |i|
    ans += ((s[i] - heikin)**2)
  end
  p (ans / n)**0.5
end