A cylindrical oil barrel is a square when its sides are expanded. It is known that the radius of the bottom of the oil barrel is 5 cm. What is the height of the oil barrel in centimeters?
一个圆柱形油桶，侧面展开是一个正方形，已知这个油桶的底面半径是5厘米，那么油桶的高是多少厘米．
<gadget id="calculator">3.14 * 5 * 2</gadget>
<output>31.4</output>

<result>31.4</result>