Year	current US$
2000	6.14269912
2001	4.11876052
2002	3.93002101
2003	3.66453089
2004	13.71152856
2005	14.27478253
2006	12.90126805
2007	6.75165796
2008	9.25432237
2009	25.98517417
2010	27.04712575
2011	25.77164432
2012	22.93548148
2013	19.20320627
2014	29.32390212
2015	31.97465436
2016	31.97672117
2017	33.47579166
2018	31.50401753
2019	28.31731741
2020	26.60398192
2021	27.70535417