Given a password $s$ with a length of $n$, we want to figure out how many different characters there are in the password.

The first line of input contains an integer $n(6 \le n \le 16)$, representing the length of the password.

The following line contains the string $s$ with the length of $n$, consisting of only visible characters(with ASCII codes between 33 and 126).

Display the number of different characters.

14
WelcomeToFDUPC
12

11
~!@#\$%^&*()
11

There are 12 different characters in the first sample, that is, 'W','e','l','c','o','m','T','F','D','U','P' and 'C'.

All characters in the second sample are different.

2018 fdupc

2018 FDUPC 程序设计校赛现场赛（网络同步赛）