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There are three types of bricks. Red colored brick of size 1x3, Green colored brick of size 1x2 and blue colored brick of size 1x1. Find out number of ways we can build a wall of size Nx3, N being the height and 3 is width, using the types of brick mentioned. Note that the bricks can be used horizontally as well as vertically. So the red and green bricks can be used in two different ways (horizontally and vertically) while the blue brick can be used only in one way (being of size 1x1, it is immaterial how you place the brick).