You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4R)-4-[3-(2-chlorophenyl)-1,2,4-oxadiazol-5-yl]-1-(2,4-dimethylphenyl)pyrrolidin-2-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H18ClN3O2
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