ABC08[C].py

def myfind(coin_self,all_coins):
    """
    目標コインとコイン全体を引数に取る。
    その目標コインが約数に取り得るコインが何枚あるか（S）を返す。
    """
    factor = -1
    for c in coins:
        if coin_self % c == 0: factor += 1
    return factor

if __name__ == '__main__':
    N = int(input())
    coins = []
    for i in range(N): coins.append(int(input()))

    accum = 0
    for coin in coins:
        S = myfind(coin,coins)
        if S % 2 == 0: accum += (S+2) / (2*S+2)
        else: accum += 0.5

    print(accum)