from itertools import permutations

n = int(input())
a = list(map(int, input().split()))
b = list(map(int, input().split()))
Pa = list(permutations(a))
Pb = list(permutations(b))
m = len(Pa)
win = 0
for i in range(m):
    for j in range(m):
        cnt = 0
        for k in range(n):
            if Pa[i][k] > Pb[j][k]:
                cnt += 1
        if cnt > n / 2:
            win += 1
print(win / m ** 2)