You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-amino-5-chloro-N-(4-ethylphenyl)-4,6-dimethylthieno[2,3-b]pyridine-2-carboxamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H18ClN3OS
assistant