The side of the cylinder is a square when expanded, and the diameter of the base of the cylinder is 5 decimeters. Find the side area of the cylinder.
圆柱的侧面展开后是正方形，圆柱的底直径是5分米，求圆柱的侧面积．
<gadget id="calculator">3.14 * 5</gadget>
<output>15.7</output>

<gadget id="calculator">15.7 * 15.7</gadget>
<output>246.49</output>

<result>246.49</result>