Year	yt
1960	4655
1961	4670
1962	4626
1963	4681
1964	4700
1965	4672
1966	4660
1967	4613
1968	4506
1969	4322
1970	4300
1971	4310
1972	4282
1973	4311
1974	4263
1975	4167
1976	4104
1977	4028
1978	3943
1979	3880
1980	3837
1981	3830
1982	3732
1983	3502
1984	3443
1985	3358
1986	3275