You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4aR,8aS)-1-benzyl-6-(2-imidazol-1-ylethyl)-2,3,4,4a,5,7,8,8a-octahydro-1,6-naphthyridine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H28N4
assistant