You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4S)-4-[3-[3-[6-(2-chlorophenoxy)pyridin-3-yl]azetidin-1-yl]-3-oxopropyl]oxolan-2-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H21ClN2O4
assistant