You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 1-[4-(4-methoxyphenyl)piperazin-1-yl]-2-[2-(trifluoromethyl)benzimidazol-1-yl]ethanone into its molecular formula.
user
C21H21F3N4O2
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