What is the percentage change in the number of shares outstanding at the end of 2018 compared to the start of 2018?
{"Outstanding, January 1, 2018": {"Number of Options": 1368772, "Weighted average exercise price": 3.12, "Weighted average remaining contractual life (years)": "", "Aggregate intrinsic value $": ""}, "Granted  2018": {"Number of Options": 401099, "Weighted average exercise price": 9.27, "Weighted average remaining contractual life (years)": "", "Aggregate intrinsic value $": ""}, "Exercised  2018": {"Number of Options": -165169, "Weighted average exercise price": 3.16, "Weighted average remaining contractual life (years)": "", "Aggregate intrinsic value $": ""}, "Expired  2018": {"Number of Options": -50002, "Weighted average exercise price": 5.48, "Weighted average remaining contractual life (years)": "", "Aggregate intrinsic value $": ""}, "Outstanding, December 31, 2018": {"Number of Options": 1554700, "Weighted average exercise price": 4.63, "Weighted average remaining contractual life (years)": 3.0, "Aggregate intrinsic value $": ""}, "Granted  2019": {"Number of Options": 410134, "Weighted average exercise price": 12.28, "Weighted average remaining contractual life (years)": "", "Aggregate intrinsic value $": ""}, "Exercised  2019": {"Number of Options": -251063, "Weighted average exercise price": 3.73, "Weighted average remaining contractual life (years)": "", "Aggregate intrinsic value $": ""}, "Expired  2019": {"Number of Options": -89550, "Weighted average exercise price": 12.55, "Weighted average remaining contractual life (years)": "", "Aggregate intrinsic value $": ""}, "Outstanding, December 31, 2019": {"Number of Options": 1624221.0, "Weighted average exercise price": 6.27, "Weighted average remaining contractual life (years)": 2.6, "Aggregate intrinsic value $": 7925643.0}, "Exercisable, December 31, 2019": {"Number of Options": 1143637.0, "Weighted average exercise price": 4.39, "Weighted average remaining contractual life (years)": 1.9, "Aggregate intrinsic value $": 7197053.0}}
outstanding_2018 = df["Outstanding, December 31, 2018"]["Number of Options"]
outstanding_2017 = df["Outstanding, January 1, 2018"]["Number of Options"]
answer = (outstanding_2018 - outstanding_2017) / outstanding_2017 * 100.0