Use a rope to tie two wine bottles with a diameter of 4 cm on the bottom surface tightly for 1 circle, at least how many centimeters of rope is needed.
用绳子将二个底面直径4厘米的酒瓶紧紧捆扎1圈，至少需要多少厘米长的绳子．
<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">12.56 + 8</gadget>
<output>20.56</output>

<result>20.56</result>