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Name the molecular formula for the molecule established as (2E,4E)-5-[(1R,6S,8R,8aS)-2,6,8-trimethyl-1,4,4a,5,6,7,8,8a-octahydronaphthalen-1-yl]penta-2,4-dienoic acid using the IUPAC nomenclature.
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C18H26O2
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