You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-methyl-4-[2-[3-methyl-4-(4-methylphenyl)piperazin-1-yl]-2-oxoethyl]phthalazin-1-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C23H26N4O2
assistant