There are 31 colorful flags on one side of the road from the beginning to the end. The distance between two adjacent colored flags is 3 meters. How long is this road?
在路的一边插彩旗，从头到尾一共插了31面，每相邻的两面彩旗相距3米，这条路有多长？
<gadget id="calculator">31 - 1</gadget>
<output>30</output>

<gadget id="calculator">30 * 3</gadget>
<output>90</output>

<result>90</result>