@staticmethod
def c():
    (n, *a) = map(int, sys.stdin.read().split())
    a = np.array(a)
    c = (n - np.count_nonzero((a[:, None] % a), axis=1))
    print(np.sum((((c + 1) // 2) / c)))
@staticmethod
def c():
    (n, *a) = map(int, sys.stdin.read().split())
    a = np.array(a)
    c = (n - np.count_nonzero((a[:, None] % a), axis=1))
    print(np.sum((((c + 1) // 2) / c)))