import itertools


def main():
    N = int(input())
    *A, = map(int, input().split())
    *B, = map(int, input().split())
    t, s = 0, 0
    for Ap in itertools.permutations(A):
        w = [a > b for a, b in zip(Ap, B)]
        t += sum(w) * 2 > N
        s += 1
    print(t/s)


if __name__ == '__main__':
    main()