You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule [2-[(5-methyl-1,2-oxazol-3-yl)amino]-2-oxoethyl] 4-oxo-3-phenylphthalazine-1-carboxylate into molecular formula.
user
C21H16N4O5
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