You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-[2-[(4-chlorophenyl)-[5-(ethylsulfanylmethyl)thiophen-2-yl]methylidene]hydrazinyl]-4-oxobutanoic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H19ClN2O3S2
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