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 2-[(9aS)-1-(benzylcarbamoyl)-2-methyl-8-(2-methylpropyl)-4,7-dioxo-3,6,9,9a-tetrahydropyrazino[2,1-c][1,2,4]triazin-6-yl]acetic acid is given. What is its corresponding molecular formula?
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C21H29N5O5
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