How much is the total operating assets as at 31 December 2019?
{"": {"2019": "RMB\u2019Million", "2018": "RMB\u2019Million"}, "Operating assets --  Mainland China": {"2019": 345721, "2018": 270373}, "Operating assets --  Others": {"2019": 168714, "2018": 83962}, "Investments --  Mainland China and Hong Kong": {"2019": 289491, "2018": 254992}, "Investments --  North America": {"2019": 76488, "2018": 44835}, "Investments --  Europe": {"2019": 29707, "2018": 37451}, "Investments --  Asia excluding Mainland China and Hong Kong": {"2019": 40139, "2018": 30148}, "Investments --  Others": {"2019": 3726, "2018": 1760}, "Investments -- ": {"2019": 953986, "2018": 723521}}
total_assets = df["Operating assets --  Mainland China"]["2019"] + df["Operating assets --  Others"]["2019"]
answer = total_assets