loop do
    n = gets.chomp.to_i
    if n == 0
        break
    end
    s = gets.split
    i = 0
    s.each do |j|
        i += j.to_f
    end
    m = i / n
    k = 0
    s.each do |l|
        k += (l.to_i - m) ** 2
    end
    a = k / n
    puts "#{sprintf("%.9f", Math.sqrt(a))}"
end