Product Code Format Check

A shop's product codes must pass three checks, in this order:

1. The code is exactly 6 characters long.
2. The first two characters are SK.
3. The last four characters form an integer from 1000 to 9999 inclusive.

Keep reading a code until it passes all three checks. Output a specific error for the first check that fails, then output Accepted and the valid code.

Input: One or more product codes. Output: An error line for each rejected code, then Accepted and the valid code.

Example:

Input:  AB
        SK12AB
        SK1000
Output: Length must be 6
        Last four must be 1000 to 9999
        Accepted
        SK1000