You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Convert the IUPAC name of a molecule 7-[(2-chlorophenyl)methyl]-1,3-dimethyl-8-pyrrolidin-1-ium-1-ylidene-5H-purine-2,6-dione into molecular formula.
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C18H21ClN5O2+
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