You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-methyl-N-[2-[(7-methyl-4-oxopyrido[1,2-a]pyrimidin-2-yl)methylsulfanyl]phenyl]benzenesulfonamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C23H21N3O3S2
assistant