from itertools import permutations

N = int(input())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
if N == 1:
    if A[0] > B[0]:
        print(1)
    else:
        print(0)
    exit()

win = 0
for a in permutations(A, N):
    for b in permutations(B, N):
        cnt = 0
        for i in range(N):
            if a[i] > b[i]:
                cnt += 1
        if cnt > N // 2:
            win += 1
print(win / (N * (N - 1))**2)