An acrobat performs riding a unicycle over a steel wire. The outer diameter of the wheel is 40 cm. During the performance, the wheel turns 25 times. How many meters of steel wire has the wheel traveled?
杂技演员表演骑独轮车过钢丝，车轮外直径40厘米，表演时车轮一共转了25圈，车轮走过了多少米长的钢丝？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3.14 * (2/5) * 25</gadget>
<output>31.4</output>

<result>31.4</result>