You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[2-chloro-4-[(4-fluorophenyl)sulfamoyl]phenoxy]-N-[4-(trifluoromethyl)phenyl]acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H15ClF4N2O4S
assistant