You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
tert-butyl 8-chloro-1,2,3,4,4a,9b-hexahydropyrido[4,3-b]indole-5-carboxylate is the IUPAC name of a molecule. Please give its molecular formula.
user
C16H21ClN2O2
assistant