You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3S,3'aR,8'aR,8'bS)-2'-methylspiro[1H-indole-3,4'-5,6,7,8,8a,8b-hexahydro-3aH-pyrrolo[3,4-a]pyrrolizin-5-ium]-1',2,3'-trione The above is the IUPAC name of a molecule. Write its molecular formula.
user
C17H18N3O3+
assistant