You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
ethyl 7,9-dithia-3-azatricyclo[6.3.0.02,6]undeca-1(8),2(6),4,10-tetraene-4-carboxylate;thieno[2,3-b]thiophene-5-carbaldehyde The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H13NO3S4
assistant