import itertools
import math

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

win_A = 0
for order_A in itertools.permutations(A):
  for order_B in itertools.permutations(B):
    point_A = 0
    point_B = 0
    for i in range(n):
      if order_A[i] > order_B[i]:
        point_A += 1
      else:
        point_B += 1
    if point_A > point_B:
      win_A += 1

num_mathces = math.factorial(n) ** 2

print(win_A / num_mathces)