# -*- coding:utf-8 -*-
import itertools
import math

if __name__ == "__main__":
	n = input()
	A = map(int,raw_input().split())
	B = map(int,raw_input().split())
	A.sort()
	B.sort()
	ans = 0
	for element_b in itertools.permutations(B,n):
		for element_a in itertools.permutations(A,n):
			temp = 0
			for a,b in zip(element_a,element_b):
				if a > b:
					temp += 1
				else:
					temp -= 1
			if temp > 0:
				ans += 1
	print ans / float(pow(math.factorial(n),2))