如图，街道ABC在点B处拐弯，在街道的一侧要等距离安装路灯，要求在点A、B、C处各安装一盏路灯，问：最少要安装多少盏路灯？

As shown in the diagram, street ABC bends at point B. Street lamps are to be installed at equal intervals along one side of the street. One street lamp is to be installed at each of points A, B and C. How many street lamps must be installed at the very least?