What was the change in the amount Outstanding at 1 April in 2019 from 2018?
{"": {"2019": "Number", "2018": "Number"}, "Outstanding at 1 April": {"2019": 35922, "2018": 44431}, "Dividend shares awarded": {"2019": "\u2013", "2018": 788}, "Forfeited": {"2019": "\u2013", "2018": -7950}, "Exercised": {"2019": -30506, "2018": -1347}, "Outstanding at 31 March": {"2019": 5416, "2018": 35922}, "Vested and outstanding at 31 March": {"2019": 5416, "2018": "\u2013"}}
outstanding_at_1_april_2019 = df["Outstanding at 1 April"]["2019"]
outstanding_at_1_april_2018 = df["Outstanding at 1 April"]["2018"]
answer = outstanding_at_1_april_2019 - outstanding_at_1_april_2018