What was the change in the Vesting of restricted stock between 2018 and 2019?
{"Common stock outstanding: -- Beginning balances": {"2019": 164588172, "2018": 177727653, "2017": 186998472}, "Common stock outstanding: -- Shares issued upon exercise of stock options": {"2019": 11348, "2018": 30832, "2017": 172620}, "Common stock outstanding: -- Shares issued under employee stock purchase plan": {"2019": 1282042, "2018": 1105400, "2017": 1228316}, "Common stock outstanding: -- Vesting of restricted stock": {"2019": 1983261, "2018": 2727229, "2017": 2102049}, "Common stock outstanding: -- Purchases of treasury stock under employee stock plans": {"2019": -489836, "2018": -793052, "2017": -550096}, "Common stock outstanding: -- Treasury shares purchased(1)": {"2019": -13854607, "2018": -16209890, "2017": -12223708}, "Common stock outstanding: -- Ending balances": {"2019": 153520380, "2018": 164588172, "2017": 177727653}}
common_stock_outstanding_vesting_of_restricted_stock_2019 = df["Common stock outstanding: -- Vesting of restricted stock"]["2019"]
common_stock_outstanding_vesting_of_restricted_stock_2018 = df["Common stock outstanding: -- Vesting of restricted stock"]["2018"]
answer = common_stock_outstanding_vesting_of_restricted_stock_2019 - common_stock_outstanding_vesting_of_restricted_stock_2018