MODE = "stdio"
require 'matrix'
include Math
line = Array.new

if(defined? MODE)
  line = STDIN.read.split("\n")
else
  tmp = '5
  70 80 100 90 20
  3
  80 80 80
  0'.split("\n")
  tmp.each{|s|
    line << s.strip
  }
end

n=0
while true
  k = line[n].to_i
  break if k == 0
  n += 1
  s = line[n].split(" ").map(&:to_f)
  m = s.inject(&:+)/k
  
  sum = 0
  s.each do |s|
    sum += (s-m)**2
  end
  
  printf("%.10f\n", (sum/k)**0.5)
  n += 1
end