What was the percentage change in the number of shares between 2018 and 2019?
{"Outstanding as of August 31, 2018": {"Shares": 8352307.0, "Weighted- Average Grant-Date Fair Value": 24.34}, "Changes during the period -- Shares granted(1)": {"Shares": 3144205.0, "Weighted- Average Grant-Date Fair Value": 25.25}, "Changes during the period -- Shares vested": {"Shares": -1983411.0, "Weighted- Average Grant-Date Fair Value": 25.07}, "Changes during the period -- Shares forfeited": {"Shares": -2347628.0, "Weighted- Average Grant-Date Fair Value": 24.78}, "Changes during the period -- Outstanding as of August 31, 2019": {"Shares": 7165473.0, "Weighted- Average Grant-Date Fair Value": 26.27}}
shares_2019 = df["Changes during the period -- Outstanding as of August 31, 2019"]["Shares"]
shares_2018 = df["Outstanding as of August 31, 2018"]["Shares"]
answer = (shares_2019 - shares_2018) / shares_2018 * 100.0