until ((n = gets.chomp.to_i) == 0)
	numbers = gets.chomp.split.map(&:to_f)
	squares = numbers.map{|n| n ** 2}
	mean = numbers.inject(:+) / n
	ss = squares.inject(:+)
	sd = Math.sqrt(ss / n - mean ** 2)
	printf("%.5f\n", sd)
end