You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
methyl-(1-methylpiperidin-1-ium-4-yl)-[(2,7,8-trimethyl-4-oxo-1H-quinolin-3-yl)methyl]azanium The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H31N3O+2
assistant