What was the percentage change in total sales between 2018 and 2019?
{"Semiconductor Equipment": {"2019": 403018, "2018": 533770, "2017": 554063}, "Industrial & Medical": {"2019": 245992, "2018": 185122, "2017": 116949}, "Data Center Computing": {"2019": 91438, "2018": "\u2014", "2017": "\u2014"}, "Telecom & Networking": {"2019": 48500, "2018": "\u2014", "2017": "\u2014"}, "Total": {"2019": 788948, "2018": 718892, "2017": 671012}}
total_2019 = df["Total"]["2019"]
total_2018 = df["Total"]["2018"]
answer = ( total_2019 - total_2018 ) / total_2018 * 100.0