You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule 7-oxa-11,21-diazatetracyclo[12.7.0.04,9.015,20]henicosa-1,3,5,8,11,13,15,17,19-nonaene .
user
C18H14N2O
assistant