from itertools import permutations
from math import factorial
n = int(input())
a = list(map(int, input().split()))
b = list(map(int, input().split()))

ans = 0
for a_ in permutations(a):
    for b_ in permutations(b):
        if sum([a_[i] > b[i] for i in range(n)]) > n // 2:
            ans += 1

print(ans / (factorial(n) ** 2))