You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(8R)-8-(3-bromo-4-hydroxy-5-methoxyphenyl)-3-(3-chlorophenyl)-6-oxo-2,4,7,8-tetrahydropyrido[2,1-b][1,3,5]thiadiazine-9-carbonitrile is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H17BrClN3O3S
assistant