Red flags are planted around the four corners of a square playground. If there are 15 red flags on each side, how many red flags are there in total?
在一个正方形操场的四周插上红旗，4个角上也插上红旗，如果每条边上插15面，那么四周一共插了多少面红旗．
<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<gadget id="calculator">60 - 4</gadget>
<output>56</output>

<result>56</result>