You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3-ethyl-1,4,6,7-tetrahydropyrazolo[4,3-c]pyridin-5-yl)-[4-(5-methylpyridin-2-yl)phenyl]methanone The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H22N4O
assistant