Year	current US$
2000	4.24681143
2001	3.23728532
2002	2.58703463
2003	7.34053202
2004	9.58715878
2005	12.61748974
2006	15.54134535
2007	18.5781372
2008	21.23207634
2009	23.32931537
2010	24.94020005
2011	25.526771
2012	30.51577487
2013	21.11442351
2014	23.83737815
2015	20.59239931
2016	21.93454594
2017	19.01603818
2018	20.18799252
2019	17.0859471
2020	20.72396043
2021	21.58856411