You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
8-[2-(3-hydroxy-2-oxo-1H-indol-3-yl)hydrazinyl]-1,3-dimethyl-7H-purine-2,6-dione is the IUPAC name of a molecule. Please give its molecular formula.
user
C15H15N7O4
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