You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[(6S)-3-cyano-6-methyl-4,5,6,7-tetrahydro-1-benzothiophen-2-yl]-2-[methyl(2-phenoxyethyl)amino]acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H25N3O2S
assistant