You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-imidazo[1,5-a]pyridin-3-ylsulfanyl-1-[4-(4-nitrophenyl)piperazin-1-yl]ethanone The above is the IUPAC name of a molecule. Write its molecular formula.
user
C19H19N5O3S
assistant