What is the difference in the total number of shares outstanding between 2018 and 2019?
{"Outstanding at September 2018": {"Number of Shares": 33800.0, "Weighted Average Exercise Price": 77.85}, "Granted": {"Number of Shares": 5450.0, "Weighted Average Exercise Price": 84.0}, "Exercised": {"Number of Shares": -2800.0, "Weighted Average Exercise Price": 79.22}, "Forfeited/Expired": {"Number of Shares": "\u2014", "Weighted Average Exercise Price": "\u2014"}, "Outstanding at September 2019": {"Number of Shares": 36450.0, "Weighted Average Exercise Price": 78.67}}
outstanding_2019 = df["Outstanding at September 2019"]["Number of Shares"]
outstanding_2018 = df["Outstanding at September 2018"]["Number of Shares"]
answer = outstanding_2019 - outstanding_2018