You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R)-2-[(2-chloro-2-fluoroacetyl)amino]-N-[4-(3-chloro-4-fluoroanilino)quinazolin-6-yl]-4-methylsulfanylbutanamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H19Cl2F2N5O2S
assistant