The stationery store is running promotional activities, and each pencil is 0.5 yuan. If you buy 3 pencils at a time, you will get 1 as a gift. Xiao Ming needs 12 pencils. What is the minimum payment.
文具店搞促销活动，每支铅笔0.5元，如果一次购买3支就赠送1支，小明需要12支，至少要付多少元．
<gadget id="calculator">0.5 * 9</gadget>
<output>4.5</output>

<result>4.5</result>