You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the compound with this IUPAC name (4S)-6-methoxy-9-nitro-4-pyridin-4-yl-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline ?
user
C18H17N3O3
assistant