Use 40 yuan to buy three kinds of exercise books with unit prices of 2 yuan, 5 yuan and 11 yuan, at least one of each kind, and the money is just spent. How many different purchasing methods are there?
用40元钱购买单价分别为2元、5元和11元的三种练习本，每种至少买一本，而且钱恰好花完．则不同的购买方法有多少种．
<gadget id="calculator">1 + 1 + 3</gadget>
<output>5</output>

<result>5</result>