You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named N-methyl-N-(5-prop-2-enyl-1,2,3,4,4a,9b-hexahydropyrido[4,3-b]indol-8-yl)benzenesulfonamide by IUPAC nomenclature, provide its molecular formula.
user
C21H25N3O2S
assistant