What was the change in sales of Industrial & Medical products 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}}
industrial_medical_2019 = df["Industrial & Medical"]["2019"]
industrial_medical_2018 = df["Industrial & Medical"]["2018"]
answer = industrial_medical_2019 - industrial_medical_2018