You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Provide the molecular formula for the IUPAC named substance 2-[2-ethyl-5-(4-ethylphenyl)-4-oxothieno[2,3-d]pyrimidin-3-yl]-2-methylpropanoic acid .
user
C20H22N2O3S
assistant