You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2,4-dichlorophenyl)-[2-[3-(3-methoxyphenyl)-1,2,4-oxadiazol-5-yl]piperidin-1-yl]methanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H19Cl2N3O3
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