from itertools import permutations

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

wcnt = 0
bcnt = 0
for pa in permutations(A):
  for pb in permutations(B):
    w = 0
    for a,b in zip(pa,pb):
      if a > b:
        w +=1
    if w > N // 2:
      wcnt += 1
    bcnt += 1
print(wcnt / bcnt)