Year	Number
2004-01-01	21
2005-01-01	19
2006-01-01	18
2007-01-01	19
2008-01-01	21
2009-01-01	21
2010-01-01	20
2011-01-01	20
2012-01-01	20
2013-01-01	20
2014-01-01	20
2015-01-01	20
2016-01-01	20