You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2S)-2-amino-5-[[5-amino-2-[(5-cyanopyrazin-2-yl)amino]pyridin-4-yl]amino]-N-phenylpentanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H23N9O
assistant