If the perimeter of a square is 8 decimeters, what is the area of a circle whose radius is the side length of the square?
一个正方形的周长是8分米，以这个正方形的边长为半径的圆的面积是多少平方分米．
<gadget id="calculator">8 / 4</gadget>
<output>2</output>

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

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

<result>12.56</result>