Cycle through the following operations one at a time until no further operations can be performed:

1. If the string prefix is 'bc', delete the first two characters and append 'aa' to the end.
2. If the string prefix is 'aa', remove the first character.
3. If the string starts with 'ac', replace the first two characters with 'zz'.
4. If the string contains an even number of 'b's (and at least one 'b'), append 'ab' at the end.
5. If the string prefix is 'ab', replace it with 'ca'.
6. If the string prefix is 'cb', replace it with 'aa' and delete the last character.

For the string "cbbcbbaabbcb", what is the final string after performing all operations?

Provide your answer as a string in the following format:

<<< "some_final_string" >>>
