from math import factorial
import itertools

def init():
  n = int(input())
  A = map(int, input().split())
  A = list(itertools.permutations(A))
  B = map(int, input().split())
  B = list(itertools.permutations(B))
  return A, B

def fullsearch():
  A, B = init()
  win = 0
  for a, b in itertools.product(A, B):
    a_crt = 0
    b_crt = 0
    for _a, _b in zip(a, b):
      if _b < _a:
        a_crt += 1
      else:
        b_crt += 1
    if b_crt < a_crt:
      win += 1
  ans = win / len(A)**2
  return ans

if __name__ == "__main__":
  ans = fullsearch()
  print(ans)