If a 1-meter-long rope is wrapped around a tree trunk, there will be an extra 0.215 meters. What is the approximate diameter of this tree?
用一条长1米的绳子绕一颗树干一圈后还多出0.215米，这棵树的直径大约是多少？
<gadget id="calculator">1 - 0.215</gadget>
<output>0.785</output>

<gadget id="calculator">0.785 / 3.14</gadget>
<output>0.25</output>

<result>0.25</result>