Year	Number
1960	-1
1961	-1
1962	-4
1963	-7
1964	-7
1965	-7
1966	-7
1967	-7
1968	-7
1969	-7
1970	-7
1971	-7
1972	-7
1973	-7
1974	-6
1975	-6
1976	-6
1977	-6
1978	-2
1979	-2
1980	-2
1981	-1
1982	-1
1983	-1
1984	-1
1985	-1
1986	-1
1987	-1
1988	-1
1989	-1
1990	-1
1991	-1
1992	-1
1993	-1
1994	-1
1995	-1
1996	-1
1997	-1
1998	-1
1999	-1
2000	8
2001	8
2002	8
2003	8
2004	8
2005	8
2006	8
2007	7
2008	7
2009	7
2010	7
2011	7