You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[(3R)-3-(9H-fluoren-9-ylmethoxycarbonylamino)-1,2,4,9-tetrahydrocarbazol-3-yl] formate is the IUPAC name of a molecule. Please give its molecular formula.
user
C28H24N2O4
assistant