PROGRAMMING:Task 10-01-02 legal C identifier
Task 10-01-02 legal C identifier
###Task description
```
Given a string that does not contain white space, please judge whether it is a legal identifier of C language.
C language identifier requirements:
1. Non reserved words;
2. Contain only letters, numbers and underscores (").
3. Don't start with a number.
```
###Input format:
```
One line, containing a string, the string does not contain any white space characters, and the length is not greater than 20.
```
###Output format:
```
If it is the legal identifier of C language, it will output yes, otherwise it will output No.
```
###Input example:
```in
RKPEGX9R; TWyYcp
```
###Output example:
```out
no
```
###Title Source
This topic is selected from openjudge website http://noi.openjudge.cn/ch0107/06/
answer：If there is no answer, please comment
###Task description
```
Given a string that does not contain white space, please judge whether it is a legal identifier of C language.
C language identifier requirements:
1. Non reserved words;
2. Contain only letters, numbers and underscores (").
3. Don't start with a number.
```
###Input format:
```
One line, containing a string, the string does not contain any white space characters, and the length is not greater than 20.
```
###Output format:
```
If it is the legal identifier of C language, it will output yes, otherwise it will output No.
```
###Input example:
```in
RKPEGX9R; TWyYcp
```
###Output example:
```out
no
```
###Title Source
This topic is selected from openjudge website http://noi.openjudge.cn/ch0107/06/
answer：If there is no answer, please comment