import itertools
import copy
N = int(input())
L1 = list(map(int, input().split()))
L2 = list(map(int,input().split()))
Shuffle1 = list(itertools.permutations(range(N)))
Numshu = len(Shuffle1)
Shuffle2 = copy.copy(Shuffle1)
ans = 0
for l in Shuffle1:
  for k in Shuffle2:
    i = 0
    for n in range(N):
      x = L1[l[n]]
      y = L2[k[n]]
      if x > y:
        i += 1
      else:
        pass
    if i > N/2:
      ans += 1
    else:
      pass
print(ans/(Numshu**2))