There is a telephone pole every 20 meters on one side of a road. There are 20 telephone poles at both ends. How long is the road in meters?
一条路的一侧每隔20米有一个电线杆，连两端的电线杆一起共20根，这条路长多少米．
<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<gadget id="calculator">20 * 19</gadget>
<output>380</output>

<result>380</result>