You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-(3-cyano-5,6,7,8-tetrahydro-4H-cyclohepta[b]thiophen-2-yl)-2-(3-ethylanilino)propanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H25N3OS
assistant