loop do
  sigma = 0

  n = gets.to_i
    exit 0 if n == 0
  s = gets.split(" ").map{|x| x.to_i}
  for i in 0..(s.length - 1)
    sigma += (s[i] - (s.inject(:+) / s.length)) ** 2
  end
  puts Math::sqrt(sigma / n)
end