The worker uncle intends to install street lights on one side of a 500-meter-long road (installed at both ends of the road). The distance between every two adjacent street lights is 25 meters. How many street lights should be installed on this road?
工人叔叔打算在一条长500米的道路的一侧安装路灯(道路两端都安装)，每相邻两盏路灯之间的距离是25米，这条道路一共要安装多少盏路灯．
<gadget id="calculator">500 / 25</gadget>
<output>20</output>

<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<result>21</result>