# frozen_string_literal: true

class Array # rubocop:todo Style/Documentation
  def judge
    count { |b, a| a > b } * 2 > size
  end

  def probability
    Rational(count(true), size).to_f
  end
end

def solve
  B.permutation.map { _1.zip(A).judge }.probability
end

N = gets.to_i
A, B = 2.times.map { gets.split.map(&:to_i) }

puts solve