You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named tetramethyl (1S,8R,9S,10R)-11-oxatricyclo[6.2.1.02,7]undeca-2(7),4-diene-4,5,9,10-tetracarboxylate by IUPAC nomenclature, provide its molecular formula.
user
C18H20O9
assistant