Year	current US$
1997	2720
1998	2870
1999	2990
2000	3320
2001	3600
2002	3940
2003	4670
2004	5830
2005	7390
2006	8930
2007	11230
2008	13520
2009	14120
2010	12650
2011	12740
2012	13800
2013	14850
2014	15340
2015	15110
2016	14800
2017	14870
2018	16560
2019	17580
2020	17900
2021	19910
2022	21970
2023	21970