You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-chloro-N-[(4S)-5-(4-fluoroanilino)-4-methyl-3-methylidene-5-oxopentyl]-4-methylbenzamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H22ClFN2O2
assistant