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The problem states that, A greedy king wants to build a wall around his castle with minimum cost and wall should not come closer to the castle than a certain distance. Given N Cartesian 2D points and minimum distance between castle and wall is  L .  To solve the problem , At first I build a convex hull using the points .  The wall should be L distance from castle . So, we need another 4 * acos(0.0) * L length ( Summing up all round length of each point of the convex hull ) .  Problem ::  Wall