What was the change in number of shares repurchased between 2017 and 2018?
{"Amount paid to repurchase shares": {"2019": "$  \u2014", "2018": 95125.0, "2017": 29993.0}, "Number of shares repurchased": {"2019": "\u2014", "2018": 1696.0, "2017": 422.0}, "Average repurchase price per share": {"2019": "$  \u2014", "2018": 56.07, "2017": 71.07}}
number_of_shares_repurchased_2018 = df["Number of shares repurchased"]["2018"]
number_of_shares_repurchased_2017 = df["Number of shares repurchased"]["2017"]
answer = number_of_shares_repurchased_2018 - number_of_shares_repurchased_2017