You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named ethyl (1S,3R,3aR,6aR)-1-[4-(dimethylamino)phenyl]-5-ethyl-3-methyl-4,6-dioxo-1,2,3a,6a-tetrahydropyrrolo[3,4-c]pyrrol-2-ium-3-carboxylate by IUPAC nomenclature, provide its molecular formula.
user
C20H28N3O4+
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