Xiao Ming is walking on the road. There is a row of small trees beside the road. Xiao Ming starts from the first tree and walks to the 20th tree and then returns to the original place. It is known that the distance between two adjacent trees is 4 meters, how many meters did Xiao Ming walk in total?
小明在马路上散步，马路边有一行小树，小明从第1棵树开始一直走到第20棵再返回原地．已知相邻两棵树之间的距离为4米，小明共走了多少米．
<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<gadget id="calculator">4 * 19 * 2</gadget>
<output>152</output>

<result>152</result>