import itertools

N = int(input())
A = "".join(list(map(str, input().split())))
B = "".join(list(map(str, input().split())))

a = []
b = []
for i in itertools.permutations(A):
	a.append(i)
for i in itertools.permutations(B):
	b.append(i)

a_win = 0
for i in range(len(a)):
	for j in range(len(b)):
		
		set_a = 0
		set_b = 0

		for k in range(N):
			if a[i][k] > b[j][k]:
				set_a+=1
			elif a[i][k] < b[j][k]:
				set_b+=1
		if set_a > set_b:
			a_win += 1
def num_game(n):
	if n == 1:
		return 1
	return n * num_game(n-1)

num = num_game(N)
print(a_win/num**2)