until (n = gets.to_i) == 0
  a = gets.split.map {|s| s.to_f}
  sum = 0.0
  for i in 1..n
    sum += a[i-1]
  end
  ave = sum / n.to_f
  sum = 0.0
  for i in 1..n
    sum += (a[i-1]-ave)**2
  end
  dev = (sum / n.to_f)**0.5
  printf("%.8f\n",dev)
end