You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[4-[2-[(5-ethyl-1H-imidazol-2-yl)sulfanyl]acetyl]piperazin-1-yl]-3-methylbutanenitrile is the IUPAC name of a molecule. Please give its molecular formula.
user
C16H25N5OS
assistant