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 4-chloro-6-(4-methylsulfonylphenyl)-2-pyrimidin-2-yl-7,8-dihydro-5H-pyrido[4,3-d]pyrimidine into molecular formula.
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C18H16ClN5O2S
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