What was the change in Other stock-based compensation expenses between 2017 and 2018?
{"Restricted stock units": {"2019": 53766, "2018": 84082, "2017": 42122}, "Employee stock purchase plan (1)": {"2019": 7580, "2018": 6891, "2017": 6334}, "Other": {"2019": "\u2014", "2018": 7538, "2017": 88}, "Total": {"2019": 61346, "2018": 98511, "2017": 48544}}
other_2018 = df["Other"]["2018"]
other_2017 = df["Other"]["2017"]
answer = other_2018 - other_2017