Year	Number
2004-01-01	2
2005-01-01	2
2006-01-01	2
2007-01-01	3
2008-01-01	3
2009-01-01	3
2010-01-01	3
2011-01-01	4
2012-01-01	4
2013-01-01	4
2014-01-01	3
2015-01-01	3
2016-01-01	3