There is a small circular lake in the park in the middle of the street. To make a circular railing with a diameter of 15m along the lake, how many meters of steel bars should be used at least?
街心公园有一圆形的小湖，沿着湖边要做1圈直径是15m的圆形栏杆，至少要用多少米的钢条？
<gadget id="calculator">3.14 * 15</gadget>
<output>47.1</output>

<result>47.1</result>