Roll a piece of square paper with a side length of 31.4 cm into a cylinder, and assign a base to the cylinder. What is the area of the base?
把一张边长是31.4厘米的正方形纸卷成圆柱形状，给这个圆柱配个底面，这个底面积是多少．
<gadget id="calculator">31.4 / 3.14 / 2</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<result>78.5</result>