There are 20 cards ranging from 1 to 20 on the table. Xiao Ming takes out 2 cards each time, and the number of a card is required to be 2 times more than the number of a card received, so how many cards does Xiao Ming take out at most.
桌上有1～20的20张卡片，小明每次取出2张卡片，要求一张卡片的编号是领一张卡片的2倍多2，则小明最多取出多少张卡片．
<gadget id="calculator">20 - 2</gadget>
<output>18</output>

<result>18</result>