You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named (3aS,4S,6aS)-2-benzylspiro[1,3,3a,5,6,6a-hexahydrocyclopenta[c]pyrrole-4,2'-1,3-dihydroquinazoline]-4'-one by IUPAC nomenclature, provide its molecular formula.
user
C21H23N3O
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