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

import itertools
patterns_A = list(itertools.permutations(A))
patterns_B = list(itertools.permutations(B))

win_count = 0
for p_A in patterns_A:
    for p_B in patterns_B:
        win_count_in_this_game = 0
        for i in range(N):
            win_count_in_this_game += (p_A[i] > p_B[i])
        if win_count_in_this_game * 2 > N:
            win_count += 1
import math
print(win_count / (math.factorial(N)**2))