You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule identified by (19S)-19-ethyl-19-hydroxy-14,18-dioxo-17-oxa-3,13-diazapentacyclo[11.8.0.02,11.04,9.015,20]henicosa-1(21),2(11),3,5,7,9,15(20)-heptaene-5-carboxylic acid ?
user
C21H16N2O6
assistant