You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[(6R,9aS)-2-pyrazin-2-yl-1,3,4,6,7,8,9,9a-octahydropyrido[1,2-a]pyrazin-6-yl]methanol is the IUPAC name of a molecule. Please give its molecular formula.
user
C13H20N4O
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