You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1,3-dimethyl-7-propyl-8-[(2E)-2-(pyridin-3-ylmethylidene)hydrazinyl]purine-2,6-dione is the IUPAC name of a molecule. Please give its molecular formula.
user
C16H19N7O2
assistant