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

ord = [*(0..N-1)].permutation.to_a

count = 0

ord.each do |ord_a|
	ord.each do |ord_b|
		win = 0
		
		N.times do |i|
			win += 1 if A[ord_a[i]] > B[ord_b[i]]
		end
		
		count += 1 if win > N/2
	end
end

puts (count.to_f / ((1..N).inject(:*) ** 2)).round(6)