Year	current US$
2000	6.3157666
2001	6.3632442
2002	6.41550924
2003	9.64785646
2004	7.68938286
2005	7.59888986
2006	7.91991059
2007	8.66169577
2008	8.41131655
2009	9.61720302
2010	12.43625097
2011	14.28795301
2012	15.81325402
2013	21.21898657
2014	23.20767136
2015	23.65867226
2016	25.31738086
2017	28.48208146
2018	27.84410966
2019	28.36996937
2020	21.41532599
2021	21.3130689