You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 1-[(3,5-dimethylphenyl)methyl]-4-(6-methyl-4-oxo-1H-pyridine-2-carbonyl)piperazin-2-one by IUPAC nomenclature, provide its molecular formula.
user
C20H23N3O3
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