#!/usr/bin/env ruby

if __FILE__ == $0 then
	loop do
		n = gets.chomp.to_i
		if n == 0 then
			break
		end

		s = gets.split.map(&:to_f)
		m = s.sum/s.size
		p (s.map { |x| (x-m)**2 }.sum / s.size) ** 0.5
	end
end

