You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule ethyl 2-[2,6-dichloro-4-[(Z)-3-(3-chloro-4-methylanilino)-2-cyano-3-oxoprop-1-enyl]phenoxy]acetate ?
user
C21H17Cl3N2O4
assistant