You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Provide the molecular formula for the IUPAC named substance 2-N,2-N,2-N',2-N',7-N,7-N,7-N',7-N'-octamethyl-9,9'-spirobi[fluorene]-2,2',7,7'-tetramine .
user
C33H36N4
assistant