You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5-(2-methoxyethyl)-3-methyl-2-pyridin-3-yl-7H-pyrrolo[3,2-f]benzimidazol-6-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H18N4O2
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