while line = gets do
  n = line.chomp.to_i
  if n==0
    break
  end
  s = gets.chomp.split(" ").map{|x| x.to_f}
  m = s.inject(:+) / n
  sum = 0
  for i in 1..n do
    sum += (s[i-1]-m)**2
  end
  a = (sum/n)**0.5
  printf("%f\n",a)
end
