A circular tabletop with a diameter of 80 cm, now a glass of the same size should be placed on the tabletop, find the area of the tabletop glass.
一个圆形的桌面，直径为80厘米，现在要在桌面上安放一个同样大小的玻璃，求这个桌面玻璃的面积．
<gadget id="calculator">80 / 2</gadget>
<output>40</output>

<gadget id="calculator">40 ** 2</gadget>
<output>1_600</output>

<gadget id="calculator">3.14 * 1_600</gadget>
<output>5_024</output>

<result>5_024</result>