def read_inputs
  scores = []
  loop do
    n = gets.to_i
    break if n == 0
    scores << Scores.new(gets.split(" ").map(&:to_f))
  end
  scores
end

class Scores
  def initialize(scores)
    @scores = scores
  end

  def standard_deviation
    m = average
    alpha = @scores.reduce(0) {|a, b| a + (b - m) ** 2} / @scores.size
    Math.sqrt(alpha)
  end

  private

  def average
    @scores.reduce(:+) / @scores.size
  end
end

scores = read_inputs
puts scores.map{|s| "%.8f"%s.standard_deviation}.join("\n")