You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-methyl-7-(4-methylimidazol-1-yl)-2,3,4,6-tetrahydro-1H-pyrido[1,2-a]pyrazine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C13H18N4
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