Year	Number
1973	600
1974	600
1975	600
1976	600
1977	700
1978	700
1979	500
1980	600
1981	1300
1982	1000
1983	1300
1984	1500
1985	1600
1986	1900
1987	1800
1988	1400
1989	1300
1990	1400
1991	1500
1992	1900
1993	1600
1994	1800
1995	2700
1996	2700
1997	2000
1998	2000
1999	2500
2000	2586
2018	2224
2019	2270
2020	561
2021	811