import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

import itertools

N,*AB = map(int,read().split())

A = AB[:N]
B = AB[N:]

perm_A = itertools.permutations(A)
perm_B = itertools.permutations(B)
match = 0
win = 0
for p,q in itertools.product(perm_A, perm_B):
    match += 1
    large = sum(x > y for x,y in zip(p,q))
    small = N - large
    if large > small:
        win += 1

print(win / match)