Cut out the largest circle from a square piece of paper with a side length of 4 cm. What is the area of this circle?
从一个边长是4厘米的正方形纸片里剪一个最大的圆，这个圆的面积是多少．
<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>

<result>12.56</result>