Year	Number
2004-01-01	18
2005-01-01	20
2006-01-01	21
2007-01-01	22
2008-01-01	22
2009-01-01	21
2010-01-01	22
2011-01-01	30
2012-01-01	32
2013-01-01	32
2014-01-01	32
2015-01-01	33
2016-01-01	33