import sys; input = sys.stdin.buffer.readline
sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")
import itertools

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	N = int(input())
	A = getlist()
	B = getlist()
	ans = 0
	total = 1
	for i in range(1, N + 1):
		total *= i ** 2

	P1 = list(itertools.permutations(A, N))
	P2 = list(itertools.permutations(B, N))
	for i in range(len(P1)):
		for j in range(len(P2)):
			cnt = 0
			for k in range(N):
				if P1[i][k] > P2[j][k]:
					cnt += 1

			if cnt * 2 > N:
				ans += 1

	print(ans / total)



if __name__ == '__main__':
	main()