import itertools

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

div = 0
ans = 0
for C in itertools.permutations(A):
    cnt = 0
    for c, b in zip(C, B):
        if c >= b:
            cnt += 1
    if 2 * cnt > n:
        ans += 1
    div += 1
print(ans / div)