You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3aS,4S,9bR)-4-(2-bromophenyl)-6-nitro-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H15BrN2O2
assistant