Put colorful flags around the square square. If two colored flags are inserted in the four corners, so that there are 20 colored flags on each side, how many colored flags should be prepared in total.
在正方形的广场周围插上彩旗．如果四个角都插两面彩旗，要使每边都有20面彩旗，那么一共要准备多少面彩旗．
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">80 - 4</gadget>
<output>76</output>

<result>76</result>