import itertools
from math import factorial

N = int(input())
A = tuple(map(int, input().split()))
B = tuple(map(int, input().split()))

c = 0
for p in itertools.permutations(A):
    for q in itertools.permutations(B):
        if sum(p[i] > q[i] for i in range(N)) > N // 2:
            c += 1
print(c / (factorial(N) ** 2))