Valid C Identifier

Problem Description

Given a string containing no whitespace characters, determine whether it is a valid C identifier (note: the problem guarantees that these strings are definitely not C reserved words).

A C identifier must satisfy:

1. It is not a reserved word;
2. It contains only letters, digits, and underscores (_);
3. It does not start with a digit.

Input Format

One line containing a string with no whitespace characters, of length at most $20$.

Output Format

One line: if it is a valid C identifier, output yes; otherwise output no.

Sample Input

RKPEGX9R;TWyYcp

Sample Output

no