|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|
|Crest Whitestrips 3D Vivid|Instore and online|2009|10 days|12 months|
|Crest Whitestrips 3D Advanced Vivid|Instore and online|March 2010|14 days|12 months|
|Crest Whitestrips 3D Professional Effects|Instore and online|March 2010|20 days|12 months|
|Crest 3D White 2 Hour Express|Instore and online|2010|2 hours|3 months|
|Crest 3D Intensive Professional Effects|Instore and online|2011|7 days|12 months|

Question: how many models require less than a week of use?
Answer: 2