# https://yukicoder.me/problems/199

from itertools import *
from math import factorial

N = int(input())

A = list(map(int, input().split()))
B = list(map(int, input().split()))

cnt = 0
for b in permutations(B,N):
    res = [1 if A[i] > b[i] else 0 for i in range(N)]
    if sum(res) > N//2:
        cnt += 1


f = factorial(N)
print(cnt/f)