You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule 7-[(2S)-1-[2-(5-methylthiophen-2-yl)acetyl]piperidin-2-yl]-8H-imidazo[1,2-a]pyrimidin-5-one into molecular formula.
user
C18H20N4O2S
assistant