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 1-[2-(6,7-dihydro-4H-thieno[3,2-c]pyridin-5-yl)-2-oxoethyl]-2-[(2-ethoxyphenyl)methyl]-3-ethylguanidine .
user
C21H28N4O2S
assistant