from itertools import permutations
from math import factorial

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

total = factorial(N)**2
win = 0
for Pattern_A in permutations(A):
    for Pattern_B in permutations(B):
        win_cnt = 0
        for a,b in zip(Pattern_A, Pattern_B):
            if a>b:
                win_cnt += 1
        if win_cnt > N//2:
            win+=1
print(win/total)