import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(10 ** 7)

import itertools

n = int(readline())
a = list(map(int, readline().split()))
b = list(map(int, readline().split()))
aa = list(itertools.permutations(a))
bb = list(itertools.permutations(b))
win = 0
for i in range(len(aa)):
    for j in range(len(bb)):
        cnt = 0
        for k in range(n):
            if aa[i][k] > bb[j][k]:
                cnt += 1
        if n // 2 < cnt:
            win += 1
print(win / (len(aa) ** 2))