On a square playground, 16 trees are planted on each side, and one tree is planted at each of the four corners. How many trees are planted in total?
在一个正方形操场上，每边栽16棵树，四个角各栽一颗，共栽多少棵树．
<gadget id="calculator">16 * 4</gadget>
<output>64</output>

<gadget id="calculator">64 - 4</gadget>
<output>60</output>

<result>60</result>