There is an iron wire that just surrounds a square with a side length of 5 decimeters. How many decimeters is this iron wire?
有一根铁丝，正好围城了一个边长5分米的正方形，这根铁丝长多少分米．
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<result>20</result>