lantern is hung every 2 meters on a rope. The starting point and the end point are not hung. A total of 12 lanterns are hung. How many meters is this rope?
在一根绳子上每隔2米挂一个灯笼起点和终点都不挂，一共挂了12个灯笼，这根绳子长多少米？
<gadget id="calculator">12 + 1</gadget>
<output>13</output>

<gadget id="calculator">13 * 2</gadget>
<output>26</output>

<result>26</result>