Year	Number
1961	2
1962	2
1963	2
1964	2
1965	2
1966	2
1967	3
1968	3
1969	3
1970	4
1971	4
1972	3
1973	4
1974	5
1975	10
1976	15
1977	20
1978	80
1979	85
1980	90
1981	95
1982	100
1983	110
1984	120
1985	130
1986	140
1987	150
1988	160
1989	163
1990	163
1991	165
1992	170