You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named [1-(6,7-dihydro-5H-cyclopenta[b]pyridin-7-yl)-2-(3,4-dimethylphenyl)ethyl]hydrazine by IUPAC nomenclature, provide its molecular formula.
user
C18H23N3
assistant