Uncle Zhang has a circular vegetable field with a radius of 4 meters. He wants to fence the vegetable field. What is the minimum length of the fence?
张大爷有一块半径4米的圆形菜地，他想把菜地用篱笆围起来，最少需要多长的篱笆？
<gadget id="calculator">2 * 3.14 * 4</gadget>
<output>25.12</output>

<result>25.12</result>