A regular triangle with a side equal to $$$n$$$ is drawn on a piece of paper. After that, the figure is divided into unit triangles, as shown in the figure for $$$n = 3$$$. How many different triangles can you find in this picture? Triangles are considered distinct if they differ either in size or location.

The only line contains the integer $$$n$$$ ($$$1 \le n \le 10^4$$$).
Print a single number — the number of distinct triangles.
2
5
4
27
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