You're given a sentence and your task is to classify whether the sentence is acceptable or not. Any sentence which is grammatically correct, has a naturalistic text, is written by a native speaker and which minimizes superfluous content is acceptable, otherwise unacceptable. If the sentence is acceptable then write "acceptable", otherwise "unacceptable".

Example Input: Willy is taller than that Bill is is generally believed.
Example Output: unacceptable

Example Input: Who is it that Mary likes?
Example Output: acceptable

Example Input: We have not confirmed whether the flight had been booked.
Example Output:
acceptable