A circular ring has an inner circumference of 12.56 decimeters and a ring width of 1 decimeter. What is the area of the ring?
一个圆环，内圆周长是12.56分米，环宽1分米，这个圆环的面积是多少．
<gadget id="calculator">12.56 / 3.14 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

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

<gadget id="calculator">9 - 4</gadget>
<output>5</output>

<gadget id="calculator">3.14 * 5</gadget>
<output>15.7</output>

<result>15.7</result>