You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 6,13-dibromo-14-methyl-2-piperidin-4-ylidene-4-azatricyclo[10.4.0.03,8]hexadeca-1(12),3(8),4,6,13,15-hexaene by IUPAC nomenclature, provide its molecular formula.
user
C21H22Br2N2
assistant