There are 78 street lamps installed on both sides of the main street of the county seat (without installation at both ends), one at an interval of 50 meters. What is the total length of the main street in the county seat?
县城主街道两旁安装了78盏路灯(两端都没安)，每隔50米安一盏．县城主街道长共多少米？
<gadget id="calculator">78 / 2</gadget>
<output>39</output>

<gadget id="calculator">39 + 1</gadget>
<output>40</output>

<gadget id="calculator">40 * 50</gadget>
<output>2_000</output>

<result>2_000</result>