Year	years
1970	6
1971	6
1972	6
1973	6
1974	6
1975	6
1976	6
1977	5.5
1978	5.5
1979	5.5
1980	5.5
1981	5.5
1982	5.5
1983	5.5
1984	5.5
1985	5.5
1986	5.5
1987	5.5
1988	5.5
1989	5.5
1990	5.5
1991	5.5
1992	5.5
1993	5.5
1994	5.5
1995	5.5
1996	5.5
1997	5.5
1998	5.5
1999	5.5
2000	5.5
2001	5.5
2002	5.5
2003	5.5
2004	6
2005	6
2006	6
2007	6
2008	6
2009	6
2010	6
2011	6
2012	6
2013	6
2014	6
2015	6
2016	6
2017	6
2018	6
2019	6
2020	6
2021	6
2022	6
2023	6