You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 2-[4-[4-methoxy-3-(trifluoromethyl)phenyl]piperidine-1-carbonyl]-6-oxaspiro[3.4]octan-7-one by IUPAC nomenclature, provide its molecular formula.
user
C21H24F3NO4
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