There is a circular fountain with a diameter of 12 meters in Xianjing Park. There is a stainless steel guardrail 0.5 meters outside the fountain. What is the minimum length of this guardrail?
仙景公园有一个直径为12米的圆形喷水池，在喷水池外0.5米处有一圈不锈钢护栏，这个护栏的长度最少是多少米？
<gadget id="calculator">12 + 0.5 + 0.5</gadget>
<output>13</output>

<gadget id="calculator">3.14 * 13</gadget>
<output>40.82</output>

<result>40.82</result>