You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4aZ,10aS)-1-methylsulfonyl-3-phenyl-6,7,8,9,10,10a-hexahydro-4H-cycloocta[b]pyridine is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H23NO2S
assistant