from itertools import permutations as p
from math import factorial as fact

n = int(input())
a, b = [tuple(map(int, input().split(" "))) for _ in range(2)]

count = 0
for a_i in p(a, n):
	for b_i in p(b, n):
		count += (sum(a_j > b_j for a_j, b_j in zip(a_i, b_i)) / n > 0.5)

print(count / fact(n)**2)