You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
6-chloro-2-N-(3,5-dichlorophenyl)-4-N-(1-ethylpiperidin-3-yl)quinazoline-2,4-diamine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H22Cl3N5
assistant