Year	Number
1970	28900000
1971	29200000
1972	29700000
1973	30800000
1974	31900000
1975	32500000
1976	32800000
1977	33400000
1978	33600000
1979	33800000
1980	33900000
1981	34100000
1982	33700000
1983	33300000
1984	33000000
1985	32700000
1986	32500000
1987	32300000
1988	31900000
1989	31700000
1990	31400000
1991	31100000
1992	31200000
1993	32100000
1994	32300000
1995	32200000
1996	31600000
1997	31900000
1998	33300000
1999	33100000
2000	34300000
2001	34400000
2002	34700000
2003	34900000
2004	32600000
2005	32600000
2006	32700000
2007	32100000
2008	32000000
2009	31800000
2010	31700000
2011	31200000
2012	30800000
2013	31500000
2014	31500000
2015	31500000
2016	31200000
2017	31100000
2018	31200000