What is the difference in the units of unvested restricted stock for 2019 and 2018?
{"Unvested restricted stock at January 31, 2018": {"Unreleased Restricted Stock Units (in thousands)": 5670.7, "Weighted average grant date fair value per share": 82.94}, "Granted": {"Unreleased Restricted Stock Units (in thousands)": 2250.7, "Weighted average grant date fair value per share": 144.37}, "Vested": {"Unreleased Restricted Stock Units (in thousands)": -2982.0, "Weighted average grant date fair value per share": 76.3}, "Canceled/Forfeited": {"Unreleased Restricted Stock Units (in thousands)": -681.9, "Weighted average grant date fair value per share": 94.7}, "Performance Adjustment (1)": {"Unreleased Restricted Stock Units (in thousands)": 29.9, "Weighted average grant date fair value per share": 101.74}, "Unvested restricted stock at January 31, 2019": {"Unreleased Restricted Stock Units (in thousands)": 4287.4, "Weighted average grant date fair value per share": 120.07}}
unvested_restricted_stock_2018 = df["Unvested restricted stock at January 31, 2018"]["Unreleased Restricted Stock Units (in thousands)"]
unvested_restricted_stock_2019 = df["Unvested restricted stock at January 31, 2019"]["Unreleased Restricted Stock Units (in thousands)"]
answer = unvested_restricted_stock_2018 - unvested_restricted_stock_2019