You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named N-[5-[3-[(2R)-2-(2-chloroethynyl)-2,7-dihydroxy-3,4,9,10-tetrahydrophenanthren-4a-yl]prop-1-enyl]pyridin-2-yl]acetamide by IUPAC nomenclature, provide its molecular formula.
user
C26H25ClN2O3
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