LAB: Next License Plate Number

A state's DMV needs a program to generate license plate numbers.

A license plate number consists of three letters followed by three digits.

An example would be CBJ$523.$

The plate numbers are given out in sequence.

So given the current number, the program should output the next number.

If the input is CBJ$523,$ the output should be CBJ$524.$

If the input is CBJ$999,$ the output should be CBK$000.$

For the last number ZZZ$999,$ the next is AAA$000.$