You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5-(1,3,4,6,7,8,9,9a-octahydropyrido[1,2-a]pyrazin-2-yl)-5,6,7,8-tetrahydronaphthalen-2-ol is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H26N2O
assistant