You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named N-[(E)-(4-bromo-2,3-dihydroinden-1-ylidene)amino]-4-oxo-3H-phthalazine-1-carboxamide by IUPAC nomenclature, provide its molecular formula.
user
C18H13BrN4O2
assistant