You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 1-(2-methyl-3,4-dihydro-2H-1,5-benzothiazepin-5-yl)-2-(4-methylsulfonylphenoxy)ethanone by IUPAC nomenclature, provide its molecular formula.
user
C19H21NO4S2
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