You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule (9-methyl-4-oxopyrido[1,2-a]pyrimidin-2-yl)methyl 2-[[(E)-2-phenylethenyl]sulfonylamino]acetate into molecular formula.
user
C20H19N3O5S
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