The diameter of the base of a cylinder is 4 cm, and the sides are expanded to form a square. What is the volume of the cylinder?
一个圆柱的底面直径为4厘米，侧面展开后得到一个正方形，圆柱的体积是多少．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<gadget id="calculator">3.14 * 4 * 12.56</gadget>
<output>157.7536</output>

<result>157.7536</result>