You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[[(2S)-2-methyl-3,4-dihydro-2H-1,5-benzothiazepin-5-yl]methyl]pyrido[1,2-a]pyrimidin-4-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C19H19N3OS
assistant