A new bridge is open to traffic. There are 20 colorful flags on the railings on both sides of the bridge. The distance between two adjacent colored flags is 5 meters. How long is the bridge?
一座新建大桥通车，在桥两边的栏杆上插彩旗，从头到尾共插20面，相邻两面彩旗的间隔都是5米，求这座桥长多少米？
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">9 * 5</gadget>
<output>45</output>

<result>45</result>