Year	current US$
2000	3.9108652
2001	3.83366
2002	4.78276927
2003	5.41792825
2004	5.6295423
2005	5.79834105
2006	5.18110932
2007	6.12279395
2008	7.60447232
2009	8.94553451
2010	10.66683236
2011	11.26683936
2012	13.37046678
2013	14.41165201
2014	13.61362123
2015	15.74241007
2016	17.08757997
2017	20.99161095
2018	25.01248003
2019	27.82877061
2020	30.14314963
2021	32.54070622