You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(E)-N-[[4-(3,4,6,7,8,8a-hexahydro-1H-pyrrolo[1,2-a]pyrazin-2-yl)phenyl]methyl]-4-(dimethylamino)but-2-enamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H30N4O
assistant