N = gets.to_i
A = gets.split.map(&:to_i)
B = gets.split.map(&:to_i)
total = 0
win = 0

[*0...N].permutation(N) do |listA|
  [*0...N].permutation(N) do |listB|
    total += 1
    win_cnt = 0

    listA.zip(listB) do |ia, ib|
      win_cnt += 1 if A[ia] > B[ib]
    end

    win += 1 if win_cnt > N / 2
  end
end

puts Rational(win, total).to_f.round(12)