You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name [5-[2-(2-fluoro-3-methylphenyl)ethynyl]-2-[1-(piperidin-3-ylamino)ethenyl]thiophen-3-yl]urea into its molecular formula.
user
C21H23FN4OS
assistant