Year	Number
1970	22700000
1971	23100000
1972	23700000
1973	24000000
1974	24200000
1975	24300000
1976	24300000
1977	24200000
1978	23900000
1979	22000000
1980	24700000
1981	23900000
1982	24200000
1983	23700000
1984	23700000
1985	23000000
1986	22900000
1987	22700000
1988	22200000
1989	21900000
1990	21500000
1991	21600000
1992	22200000
1993	22900000
1994	23500000
1995	23600000
1996	24000000
1997	24400000
1998	24800000
1999	24900000
2000	25100000
2001	25600000
2002	25700000
2003	26400000
2004	26700000
2005	27000000
2006	27100000
2007	27300000
2008	27300000
2009	27100000
2010	26700000
2011	26700000
2012	26700000
2013	26700000
2014	26800000
2015	26900000
2016	27200000
2017	27300000
2018	27500000