说明：  有股神吗？ 有，小赛就是！ 经过严密的计算，小赛买了一支股票，他知道从他买股票的那天开始，股票会有以下变化：第一天不变，以后涨一天，跌一天，涨两天，跌一天，涨三天，跌一天...依此类推。 为方便计算，假设每次涨和跌皆为1，股票初始单价也为1，请计算买股票的第n天每股股票值多少钱？
(Do you have a stock god? Yes, the little match is! After a tight calculation, the small race bought a stock, and he knew that the stock would have changed from the day he bought the stock: the first day, a day, a day, two days, a day, three days, a day, and so on. To facilitate the calculation, suppose that each time the price rises and falls is 1, and the initial price of the stock is 1, what is the value of the stock n per day?)