You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule 3-[(5E)-5-[(4-methyl-2,3,3a,8b-tetrahydro-1H-cyclopenta[b]indol-7-yl)methylidene]-4-oxo-2-sulfanylidene-1,3-thiazolidin-3-yl]propanoic acid .
user
C19H20N2O3S2
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