while true do
	n = STDIN.gets.chomp.to_i
	break if n == 0
    s = STDIN.gets.chomp.split(" ")
    
    sum = 0

	0.upto(n - 1) { |i|
		s[i] = s[i].to_f
		sum += s[i]
	}
	
	ave = sum / n
	
	sum2 = 0
	0.upto(n - 1) { |i|
		sum2 += (s[i] - ave) ** 2 / n
	}
	
	print Math.sqrt(sum2), "\n"

end

