You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
9-(4-benzylpiperazin-1-yl)-2-methyl-3-phenyl-5,6,7,8-tetrahydropyrazolo[5,1-b]quinazoline is the IUPAC name of a molecule. Please give its molecular formula.
user
C28H31N5
assistant