Year	US Dollars
1967	2090
1968	2520
1969	2430
1970	2400
1971	2640
1972	2660
1973	3330
1974	4600
1975	5120
1976	5620
1977	5940
1978	6820
1979	8060
1980	9240
1981	9710
1982	9240
1983	8280
1984	8120
1985	8420
1986	10350
1987	13120
1988	15480
1989	15050
1990	15390
1991	16160
1992	17430
1993	17590
1994	17690
1995	18150
1996	18020
1997	17490
1998	16890
1999	16400
2000	15990