In fiscal year ended June 30, 2018, what is the percentage constitution of the non-current operating assets in the United States among the total non-current operating assets owned by the Group?
{"Non-current operating assets -- United States": {"2019": 819227, "2018": 412112}, "Non-current operating assets -- Australia": {"2019": 18842, "2018": 16730}, "Non-current operating assets -- India": {"2019": 9286, "2018": "\u2014"}, "Non-current operating assets -- ": {"2019": 847355, "2018": 428842}}
non_current_assets_2018 = df["Non-current operating assets -- United States"]["2018"]
total_non_current_assets = df["Non-current operating assets -- "]["2018"]
answer = non_current_assets_2018 / total_non_current_assets * 100.0