Xiao Ming saw a row of willow trees on the embankment, one at a distance of 4 meters. He walked from the next one to the 20th tree. How many meters did he walk in total?
小明看到河堤上有一排柳树，每隔4米一棵，他从身边的一棵走到第20棵树下，他共走了多少米．
<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<gadget id="calculator">4 * 19</gadget>
<output>76</output>

<result>76</result>