Use 20 pieces to surround a hollow square matrix with one layer, how many pieces are there on each side.
用20枚棋子围一个一层的空心方阵，每边有多少枚棋子．
<gadget id="calculator">20 + 4</gadget>
<output>24</output>

<gadget id="calculator">24 / 4</gadget>
<output>6</output>

<result>6</result>