loop do
	n = gets.to_i
	break if n == 0
	scores = gets.split.map(&:to_i)
	sum = scores.inject(:+)
	average = sum.to_f / scores.size
	variance = scores.inject(0.0){|v, i| v + (i - average) ** 2.0} / n.to_f
	puts (variance ** (1.0/2)).round(5)
end