The street ABC turns at B, and street lamps should be installed at equal distances on one side of the street. It is required to install a street lamp at A, B, and C respectively. It is known that the length of AB is 520 meters, and the length of BC is 715 meters. This street requires at least How many street lights are installed?
街道ABC在B处拐弯，在街道的一侧要等距离装路灯，要求A、B、C处各装一盏路灯，已知AB长为520米，BC长为715米，这条街道最少要装多少盏路灯？
<gadget id="calculator">5 * 13</gadget>
<output>65</output>

<gadget id="calculator">520 / 65</gadget>
<output>8</output>

<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<gadget id="calculator">715 / 65</gadget>
<output>11</output>

<gadget id="calculator">11 + 1</gadget>
<output>12</output>

<gadget id="calculator">12 - 1</gadget>
<output>11</output>

<gadget id="calculator">9 + 11</gadget>
<output>20</output>

<result>20</result>