Table:
text: Crest Whitestrips
Summary of products
Summary of products
Model Availability Introduced Length_of_use Last_of_whiteness_
Crest Whitestrips Classic , previously Crest Whitestrips Discontinued May 2001 14 days 12 months
Crest Whitestrips Professional Discontinued 2001 10 days 12 months
Crest Whitestrips Supreme Dentist and online September 2003 21 days 18 months
Crest Whitestrips Premium Discontinued January 2004 7 days 12 months
Crest Whitestrips Pro , previously Crest Whitestrips Premium Plus Discontinued April 2005 10 days 18 months
Crest Whitestrips Renewal Discontinued January 2006 10 days 18 months
Crest Whitestrips Daily Multicare Discontinued March 2007 Daily White after using system
Crest Whitestrips Advanced Seal Discontinued February 2009 14 days 18 months

Question: How many Crest Whitestrips products have been discontinued?