Cut a square iron sheet with a side length of 4 decimeters into the largest circle, and the area of the cut part is equal to the area of the square.
把一块边长4分米的正方形铁皮剪成一个最大的圆形，剪去部分的面积是正方形面积的多少．
<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<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">16 - 12.56</gadget>
<output>3.44</output>

<gadget id="calculator">3.44 / 16</gadget>
<output>0.215</output>

<result>0.215</result>