You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-[4-(6,7,8,9-tetrahydro-5H-pyrimido[4,5-d]azepin-4-yl)piperazin-1-yl]pyrazine-2-carbonitrile The above is the IUPAC name of a molecule. Write its molecular formula.
user
C17H20N8
assistant