The students form a square to play games on the playground. There are 18 students on each side. How many students are playing games in total?
同学们在操场上围成一个正方形玩游戏，每边18个同学，一共有多少个同学在玩游戏．
<gadget id="calculator">18 * 4</gadget>
<output>72</output>

<gadget id="calculator">72 - 4</gadget>
<output>68</output>

<result>68</result>