You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[4-[(E)-(5-ethyl-2-oxo-6-thia-1,8-diazatricyclo[7.3.0.03,7]dodeca-3(7),4,8-trien-10-ylidene)methyl]phenoxy]acetic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H18N2O4S
assistant