lines = STDIN.read.split("\n")
loop do
    size = lines.shift.to_f
    break if size == 0
    nums = lines.shift.split.map(&:to_i)
    mean = nums.reduce(0){|sum, n| sum + n} / size
    a = (nums.reduce(0){|sum, n| sum + (n - mean) ** 2} / size) ** 0.5
    puts "%.8f" % a
end