Year	Number
1961	3
1962	5
1963	10
1964	12
1965	12
1966	12
1967	12
1968	13
1969	13
1970	13
1971	13
1972	14
1973	14
1974	14
1975	14
1976	15
1977	15
1978	15
1979	16
1980	16
1981	16
1982	17
1983	17
1984	17
1985	18
1986	18
1987	18
1988	19
1989	19
1990	19
1991	19
1992	19
1993	19
1994	19
1995	19
1996	19