一个旅店总共m间房间，先按顺序给定旅客到来和离开的顺序，当有人来时，已经注满，则这人不能入住，输出一共有多少人不能入住

输入：m（表房间数）

SFADSF(字母表示旅客)

输出：未能入住的人数



样例：

输入：3

GACCBDDBAGEE



输出：1

-A total of m a hotel room, press the order given sequence passenger arrival and departure, when someone comes, has been filled, then this person can not stay, the output of the total number of people can not stay

 　Input: m (Table Room)

           　SFADSF (letters passengers)

 　Output: The number could not be admitted in

 

 　Sample:

 　Input: 3

           　GACCBDDBAGEE

 　Output:

           　1