from itertools import permutations
N = int(input())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

aw = 0
x = 0
for pa in permutations(A):
    for pb in permutations(B):
        x += 1   
        ac = 0
        for i in range(N):
            if pa[i] > pb[i]:
                ac += 1
        if ac > N//2:
            aw += 1

print(aw/x)