You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
9-methyl-5-(2-piperazin-1-ylethyl)-9,11-diazatetracyclo[9.2.2.02,10.03,8]pentadeca-2(10),3(8),4,6-tetraene is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H28N4
assistant