You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule 2-(5-pyrazin-2-yl-1H-pyrazolo[3,4-c]pyridin-3-yl)-4-pyridin-4-yl-1H-imidazo[4,5-c]pyridine .
user
C21H13N9
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