[{"from": "human", "value": "Given SMILES, write its number-averaged molecular weight at normal measurement conditions.. ->  O=C1C2=C(CCCCCC)SC(CCCCCC)=C2C(C3=C(C)SC(C4=CC5=C(C(OCC(CCCC)CC)=C(C=C(C)S6)C6=C5OCC(CCCC)CC)S4)=C31)=O\n"}, {"from": "gpt", "value": " 18.8\n"}]