There is a square playground with 4 trees planted on each side and 1 tree of each kind at the four corners. How many trees were planted in total?
有一正方形操场，每边都栽种4棵树，四个角各种1棵．问共种树多少棵？
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<result>12</result>