What is the increase/ (decrease) in Interest expense, net of interest income from 2018 to 2019?
{"Net income (loss)": {"2019": -19931, "2018": -50571, "2017": 65299}, "Add (subtract): -- Interest expense, net of interest income": {"2019": 136660, "2018": 134578, "2017": 129786}, "Add (subtract): -- Income tax benefit": {"2019": -3714, "2018": -24127, "2017": -124927}, "Add (subtract): -- Depreciation and amortization": {"2019": 381237, "2018": 432668, "2017": 291873}, "Add (subtract): -- EBITDA": {"2019": 494252, "2018": 492548, "2017": 362031}, "Adjustments to EBITDA: -- Other, net (1)": {"2019": -8847, "2018": 549, "2017": 19314}, "Adjustments to EBITDA: -- Investment distributions (2)": {"2019": 35809, "2018": 39078, "2017": 29993}, "Adjustments to EBITDA: -- Gain on extinguishment of debt": {"2019": -4510, "2018": "\u2014", "2017": "\u2014"}, "Adjustments to EBITDA: -- Non-cash, stock-based compensation": {"2019": 6836, "2018": 5119, "2017": 2766}, "Adjustments to EBITDA: -- Adjusted EBITDA": {"2019": 523540, "2018": 537294, "2017": 414104}}
interest_expense_2019 = df["Add (subtract): -- Interest expense, net of interest income"]["2019"]
interest_expense_2018 = df["Add (subtract): -- Interest expense, net of interest income"]["2018"]
answer = interest_expense_2019 - interest_expense_2018