Username Validator

This problem requires you to implement a username validator. The validator must check if the provided username satisfies all the following criteria:

• The length of the username must satisfy the inequality \(5 \leq |username| \leq 15\).
• The username must start with an English letter (a-z or A-Z).
• The username can contain only English alphabets (a-z, A-Z) and digits (0-9).

If the username satisfies all the conditions, output VALID; otherwise, output INVALID.

Your solution should read the username from standard input and write the result to standard output.

inputFormat

The input consists of a single line containing the username string.

outputFormat

Output a single line: VALID if the username meets all the conditions, or INVALID otherwise.

user123

VALID