You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
6-[(4aR,8aS)-4-benzyl-2,3,4a,5,6,7,8,8a-octahydroquinoxalin-1-yl]pyrazine-2-carbonitrile The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H23N5
assistant