You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-[(3aR,4R,9bS)-7-chloro-6-methyl-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinolin-4-yl]benzoic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H18ClNO2
assistant