What is the difference in weighted-average grant date fair value between granted and forfeited shares?
{"Unvested shares at December 31, 2018": {"Number of Shares": 1924.0, "Weighted- Average Grant Date Fair Value": 40.81}, "Granted": {"Number of Shares": 390.0, "Weighted- Average Grant Date Fair Value": 56.74}, "Forfeited": {"Number of Shares": -562.0, "Weighted- Average Grant Date Fair Value": 41.29}, "Vested": {"Number of Shares": "\u2014", "Weighted- Average Grant Date Fair Value": "\u2014"}, "Unvested shares at December 31, 2019 1": {"Number of Shares": 1752.0, "Weighted- Average Grant Date Fair Value": 44.21}}
granted_fair_value = df["Granted"]["Weighted- Average Grant Date Fair Value"]
forfeited_fair_value = df["Forfeited"]["Weighted- Average Grant Date Fair Value"]
answer = granted_fair_value - forfeited_fair_value