#!/usr/bin/env python
# -*- coding: utf-8 -*-
import itertools
from math import factorial

n = int(input())
a = [int(i) for i in input().split()]
b = [int(i) for i in input().split()]

scnt = 0
for i in itertools.permutations(a, n):
    for j in itertools.permutations(b, n):
        acnt = bcnt = 0
        for x, y in zip(i, j):
            if x > y: acnt += 1
            else: bcnt += 1
        if acnt > bcnt: scnt += 1

print(scnt / factorial(n) ** 2)