i = 0
ARGF.each_line do |line|
  i += 1
  break if line == 0
  next if i % 2 == 1

  s = line.split.map(&:to_f)
  
  sum = 0
  s.each do |j|
    sum += j
  end
  avr = sum / s.size
  
  x = 0
  s.each do |j|
    x += (j - avr)**2
  end
  a = Math.sqrt(x / s.size)
  puts a
end