You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5-(5,7-diphenyl-11b,12-dihydroindolo[2,3-b]carbazol-2-yl)-7-phenylindolo[2,3-b]carbazole is the IUPAC name of a molecule. Please give its molecular formula.
user
C54H36N4
assistant