You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(5aR,6R,9aS)-8-isocyano-6,9a-dimethyl-1-(4-methylphenyl)-3-phenyl-4,5,5a,6-tetrahydrobenzo[g]indazol-7-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C27H25N3O
assistant