You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4R,6S)-3,6-dimethyl-4-(4-phenylmethoxyphenyl)-4,8-dihydro-2H-pyrazolo[3,4-e][1,4]thiazepin-7-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H21N3O2S
assistant