You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule ethyl (1R,3R,3aR,6aR)-5-ethyl-3-methyl-4,6-dioxo-1-(4-propan-2-ylphenyl)-1,2,3a,6a-tetrahydropyrrolo[3,4-c]pyrrole-3-carboxylate .
user
C21H28N2O4
assistant