You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1H-indol-2-yl-[4-[1-(5-thiophen-2-yl-1,3,4-oxadiazol-2-yl)ethyl]piperazin-1-yl]methanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H21N5O2S
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