You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(1R,9R,13R)-10-(4-ethoxyphenyl)-9,13-dimethyl-4-nitro-8-oxa-10,12-diazatricyclo[7.3.1.02,7]trideca-2(7),3,5-triene-11-thione The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H21N3O4S
assistant