Year	years
1970	2
1971	2
1972	2
1973	2
1974	2
1975	2
1976	2
1977	2
1978	2
1979	2
1980	2
1981	2
1982	2
1983	2
1984	2
1985	2
1986	2
1987	2
1988	2
1989	2
1990	2
1991	2
1992	2
1993	2
1994	2
1995	2
1996	2
1997	2
1998	2
1999	3
2000	3
2001	3
2002	3
2003	3
2004	3
2005	3
2006	3
2007	3
2008	3
2009	3
2010	3
2011	3
2012	3
2013	3
2014	3
2015	3
2016	3
2017	3
2018	3