Tie a stack of books with a rope and make a circle, the rope is still 2 decimeters long, and then connect another 2 decimeters long rope, just enough to wrap around the stack of books again, how long is this rope?
用一根绳子捆一叠书绕一圈，绳子还长2分米，再接一根2分米长的绳子，就正好又能绕这叠书一圈，这根绳子原来有多长？
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">8 - 2</gadget>
<output>6</output>

<result>6</result>