Year	Number
1970	32600000
1971	33100000
1972	33500000
1973	33700000
1974	33600000
1975	33400000
1976	33000000
1977	32500000
1978	31800000
1979	31200000
1980	30700000
1981	30400000
1982	30100000
1983	30100000
1984	30400000
1985	30900000
1986	31600000
1987	32200000
1988	32600000
1989	33100000
1990	33200000
1991	33400000
1992	33300000
1993	33400000
1994	33600000
1995	34100000
1996	34300000
1997	34700000
1998	35500000
1999	36600000
2000	37200000
2001	38000000
2002	37800000
2003	37100000
2004	35100000
2005	33400000
2006	32300000
2007	31300000
2008	30000000
2009	29200000
2010	28500000
2011	27900000
2012	27300000
2013	29200000
2014	29200000
2015	28800000
2016	29100000
2017	30000000
2018	30500000