You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[1-ethyl-4-[4-(4-methoxyphenyl)piperazin-1-yl]-6-methyl-2-sulfanylidenepyrimidin-5-yl]ethanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H26N4O2S
assistant