After a circle is divided into several equal parts, it is assembled into an approximate rectangle, and the circumference is increased by 4 decimeters. What is the area of the original circle in square decimeters?
将一圆平均分成若干等份后，拼成一个近似的长方形，周长增加了4分米，原来圆的面积是多少平方分米．
<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>