You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(5R)-5-[3-[4-(1,3-benzoxazol-2-yl)piperidin-1-yl]-3-oxopropyl]-5-ethylpyrrolidin-2-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H27N3O3
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