What is the sum of the three least contributing property segments in 2019?
{"U.S.": {"2019": 55, "2018": 51, "2017": 55}, "Asia": {"2019": 16, "2018": 21, "2017": 17}, "Africa": {"2019": 8, "2018": 7, "2017": 7}, "Europe": {"2019": 2, "2018": 2, "2017": 2}, "Latin America": {"2019": 18, "2018": 17, "2017": 18}}
europe = df["Europe"]["2019"]
africa = df["Africa"]["2019"]
asia = df["Asia"]["2019"]
answer = europe + africa + asia