There is a rural road, and street lamps are installed on one side of the road (both ends are installed), one lamp is installed every 50 meters, and a total of 40 lamps are installed. How long is this road in meters?
有一条乡村公路，在公路的一侧安路灯(两端都安)，每隔50米安一盏，一共安了40盏．这条公路长多少米．
<gadget id="calculator">40 - 1</gadget>
<output>39</output>

<gadget id="calculator">39 * 50</gadget>
<output>1_950</output>

<result>1_950</result>