What is the molecular formula of the molecule identified by [(3aR,4R,6S,6aR,9aR,9bR)-9-methyl-3-methylidene-2-oxospiro[4,5,6a,7,9a,9b-hexahydro-3aH-azuleno[4,5-b]furan-6,2'-oxirane]-4-yl] furan-3-carboxylate ?