loop do
  n = gets.to_i
  break if n == 0 
  data = gets.split.map{|e|e.to_i}
  sum = data.inject{|sum,val| sum += val}
  mean = 1.0*sum/n

  variance = 0.0
  for elem in data
    variance += (elem-mean)**2/n
  end

  puts Math.sqrt(variance)
end