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".

I saw him leaving the main building.
acceptable

The ship's sinking to collect the insurance was very devious.
unacceptable

Bill believes that Anna and he are similar.

acceptable