You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-piperidin-4-yl-7,8,9,10-tetrahydro-1H-pyrimido[1,2-b]indazol-2-one;hydrochloride is the IUPAC name of a molecule. Please give its molecular formula.
user
C15H21ClN4O
assistant