You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
methyl (1R,3S,3aR,6aS)-3-benzyl-5-methyl-4,6-dioxo-1-pyridin-4-yl-1,2,3a,6a-tetrahydropyrrolo[3,4-c]pyrrole-3-carboxylate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H21N3O4
assistant