Cut out the largest circle on a rectangular cardboard with a length of 28cm and a width of 26cm. What is the radius of this circle?
在长28cm，宽26cm的长方形纸板上剪出一个最大的圆，这个圆的半径是多少．
<gadget id="calculator">26 / 2</gadget>
<output>13</output>

<result>13</result>