You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-methyl-4-(1-propylpiperidin-4-yl)-6,7,8,9-tetrahydropyrazolo[3,4-c]isoquinolin-5-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C19H28N4O
assistant