Description

Given a string that does not contain any whitespace characters, determine whether it is a valid C language identifier (Note: The problem guarantees that these strings are definitely not C language reserved keywords).

The requirements for a C language identifier are:

1. It must not be a reserved keyword.
2. It can only contain letters, digits, and underscores ("_").
3. It must not start with a digit.

Input Format

One line containing a string with no whitespace characters and a length not exceeding 20.

Output Format

One line. If it is a valid C language identifier, output yes; otherwise, output no.

## Sample Input 1
example_1

## Sample Output 1
yes

## Sample Input 2
123example

## Sample Output 2
no

RKPEGX9R;TWyYcp

no