You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[4-[3-oxo-4,9-di(propan-2-yloxy)-1H-benzo[f]isoindol-2-yl]phenyl]butanoic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C28H31NO5
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