You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[(2S)-6,7-dimethyl-3-oxo-2,4-dihydro-1H-quinoxalin-2-yl]-N-(2,3-dimethylphenyl)acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H23N3O2
assistant