Wrap a thread around a pencil exactly 100 times. It is known that the diameter of the bottom of the pencil is 0.8 cm. Find the length of this thin string.
把一根线绕在铅笔上，正好绕了100圈，已知铅笔的底面直径是0.8厘米，求这根细绳长度．
<gadget id="calculator">3.14 * 0.8 * 100</gadget>
<output>251.2</output>

<result>251.2</result>