Year	US Dollars
1971	0.22464
1972	3.22669
1973	5.92411
1974	7.28452
1975	14.1255
1976	6.43898
1977	9.88536
1978	11.98287
1979	13.70047
1980	14.64689
1981	12.23715
1982	14.72605
1983	10.90949
1984	11.85705
1985	10.24134
1986	13.10641
1987	16.11101
1988	13.56145
1989	14.13489
1990	16.69565
1991	14.75813
1992	13.46834
1993	10.27493
1994	11.97726
1995	8.77053
1996	8.04893
1997	7.07273
1998	7.87733
1999	7.93208
2000	7.5572
2001	6.97537
2002	6.01909
2003	9.5367
2004	10.24067
2005	8.88224
2006	7.20626
2007	9.07837
2008	12.14285
2009	7.38043
2010	8.94481
2011	9.57
2012	14.16294
2013	17.09789
2014	15.5336
2015	16.4285
2016	15.85147
2017	23.37399
2018	18.60146
2019	26.47227
2020	32.09795
2021	29.76577