You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[[4-(6-hydroxynaphthalen-2-yl)-2,3,3a,8b-tetrahydro-1H-cyclopenta[b]indol-7-yl]methyl]-3-methylbutanenitrile is the IUPAC name of a molecule. Please give its molecular formula.
user
C27H28N2O
assistant