You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
methyl 2-[(8aS)-3,4,6,7,8,8a-hexahydro-1H-pyrrolo[1,2-a]pyrazin-2-yl]-5-nitrobenzoate is the IUPAC name of a molecule. Please give its molecular formula.
user
C15H19N3O4
assistant