You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
6-chloro-1-ethyl-3-[3-(5-methyl-1H-pyrazol-3-yl)piperidine-1-carbonyl]quinolin-4-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H23ClN4O2
assistant