You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[2-(2,6-dimethylanilino)-2-oxoethyl]-2-(1,3-dioxoisoindol-2-yl)-N-methylacetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H21N3O4
assistant