What is the proportion of exercisable options over outstanding options for the year ended in December 31, 2019?
{"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}}
exercisable_december_31_2019 = df["Exercisable, December 31, 2019"]["Number of Options"]
outstanding_december_31_2019 = df["Outstanding, December 31, 2019"]["Number of Options"]
answer = exercisable_december_31_2019 / outstanding_december_31_2019