On Children's Day on June 1st, a colorful flag is placed every 2 meters on the side of the main road of the school. A total of 20 sides have been inserted from beginning to end. How long is this main road in meters?
"六一"儿童节，学校主干道一旁每隔2米插一面彩旗．从头到尾一共插了20面．这条主干道长多少米．
<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<gadget id="calculator">19 * 2</gadget>
<output>38</output>

<result>38</result>