You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
19-ethyl-19-hydroxy-3,13-diazapentacyclo[11.8.0.02,11.04,9.015,20]henicosa-1(21),2,4,6,8,10,15(20)-heptaene-14,17-dione The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H18N2O3
assistant