You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-[(8-chloro-5-phenyl-4,5-dihydro-[1,2,4]triazolo[3,4-d][1,5]benzothiazepin-1-yl)methyl]morpholine is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H21ClN4OS
assistant