You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-[[(8aS)-5,8-dioxo-1,3,6,8a-tetrahydro-[1,3]thiazolo[3,4-a]pyrazin-7-yl]methyl]-N-(3-propylsulfanylpropyl)benzamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H27N3O3S2
assistant