Square paper with a side length of 8 decimeters encloses a cylindrical paper tube (not counting the joints), what is the side area of the paper tube?
边长是8分米的正方形纸围成一个圆柱形纸筒(接头处不计)，这个纸筒的侧面积是多少．
<gadget id="calculator">8 * 8</gadget>
<output>64</output>

<result>64</result>