import sys
import itertools
import numpy as np

input = sys.stdin.readline


def S():
    return input().rstrip()


def I():
    return int(input())


def MI():
    return map(int, input().split())


n = I()
ac = list(MI())
bc = list(MI())

ans = 0
count = 0
for a in itertools.permutations(ac):
    for b in itertools.permutations(bc):
        count += 1
        result = np.array(a) - np.array(b)
        win = np.sum(result > 0)
        lose = np.sum(result < 0)
        if win > lose:
            ans += 1

print(ans / count)