<image>Someone has light bulbs in 4 different colors (an ample supply of each color) and wants to install one light bulb at each of the 6 points A, B, C, A_{1}, B_{1}, C_{1} as shown in the figure. It is required that the light bulbs at both ends of the same line segment are of different colors. How many installation methods are there if each color is used at least once? (Answer with a number.)
