You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(6-methyl-2-pyridin-3-ylpyrimidin-4-yl)-1,3,3a,4,7,7a-hexahydroisoindole The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H20N4
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