
def avg(data,n)
  sum = 0
  data.each do |d|
    sum = sum + d
  end
  (sum/n).to_f
end

def variance (data,n)
  sum_v = 0
  m = avg(data,n)
  data.each do |s|
    sum_v = sum_v + (s-m)**2
  end
  (sum_v/n).to_f
end

def stdev (data,n)
  Math.sqrt(variance(data,n)).to_f
end

while true
  n = gets.to_i
  break if (n==0)
  data = gets.split().map(&:to_i)
  printf("%0.8f\n", stdev(data, n))
end