You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (7S,9aS)-2,7-dimethyl-1,3,4,6,7,8,9,9a-octahydropyrido[1,2-a]pyrazine by IUPAC nomenclature, provide its molecular formula.
user
C10H20N2
assistant