Cut a cylindrical wooden block vertically along the diameter of the bottom surface into two equal half cylinders, the surface area is increased by 520 square centimeters, find the original lateral area of the wooden block.
把一个圆柱形木块沿底面直径垂直切成两个相等的半圆柱体，表面积增加520平方厘米，求原来这个木块的侧面积．
<gadget id="calculator">520 / 2</gadget>
<output>260</output>

<gadget id="calculator">3.14 * 260</gadget>
<output>816.4</output>

<result>816.4</result>