You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-(3-chlorophenyl)-4-[4-(4-fluoropiperidin-1-yl)-4-oxobutyl]-2-methyl-3-oxopiperazine-1-carboxamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H28ClFN4O3
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