It is known that the diameter of the small circle is 4 cm, and the width of the ring wall is 1 cm. What is the area of the ring in square centimeters?
已知小圆的直径是4厘米，环壁宽1厘米，圆环的面积是多少平方厘米？
<gadget id="calculator">4 / 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>