You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-[2-[4-(1,2-benzothiazol-3-yl)piperazin-1-yl]ethyl]-9-chloro-2-methyl-6,7,8,9-tetrahydropyrido[1,2-a]pyrimidin-4-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C22H26ClN5OS
assistant