# yukicoder133
from math import factorial
from itertools import permutations
n = int(input())
a = list(map(int, input().split()))
b = list(map(int, input().split()))
ans = 0
for a_order in permutations(a):
    for b_order in permutations(b):
        cnt = 0
        for i in range(n):
            if a_order[i] > b_order[i]:
                cnt += 1
        if cnt > n // 2:
            ans += 1
ans /= (factorial(n))**2
print(ans)