Year	Number
1961	12
1962	12
1963	13
1964	14
1965	17
1966	19
1967	20
1968	22
1969	22
1970	22
1971	22
1972	22
1973	22
1974	22
1975	22
1976	22
1977	23
1978	24
1979	25
1980	25
1981	24
1982	23
1983	22
1984	21
1985	20
1986	20
1987	19
1988	18
1989	17
1990	16
1991	15
1992	14
1993	13
1994	13
1995	13
1996	12
1997	12
1998	12
1999	12