Cut the largest circle out of a square whose side length is 4 cm. What is the area of the circle in square centimetres?
在边长是4厘米的正方形中剪下一个最大的圆，圆的面积是多少平方厘米．
<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>

<result>12.56</result>