 pack of cigarettes per year or a half of a pack of cigarettes for two years, you figure it out. So it's 20 pack years smoking. So if you smoke, for example, one pack for 20 years or two packs for 10 years, that's all 20 pack years. So if you're age 50 to 80, you have a 20 pack year smoking history and currently smoke or you've quit within the past 15 years smoking.