You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[3-[(8aS)-1,4-dioxo-6,7,8,8a-tetrahydro-3H-pyrrolo[1,2-a]pyrazin-2-yl]-2-oxopyrrolidin-1-yl]acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C13H18N4O4
assistant