Draw the largest circle inside the square. Given that the side length of the square is 4 cm, what is the area of the circle in square centimeters?
正方形内画一个最大的圆，已知正方形的边长是4厘米，圆的面积是多平方厘米？
<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>