You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named 1-[4-[5-amino-6-(1H-benzimidazol-2-yl)pyrazin-2-yl]piperazin-1-yl]-2-methoxyethanone is given. What is its corresponding molecular formula?
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C18H21N7O2
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