import sys
#sys.setrecursionlimit(n)
import heapq
import re
import bisect
import random
import math
import itertools
from collections import defaultdict, deque
from copy import deepcopy
from decimal import *

n = int(input())
a = list(map(int, input().split()))
b = list(map(int, input().split()))

aa = list(itertools.permutations(a))
bb = list(itertools.permutations(b))

win_count = 0
for ta in aa:
  for tb in bb:
    if ta[0] > tb[0] and ta[1] > tb[1]:
      win_count += 1
print(win_count / (len(aa) * 2))