Consider a figure similar to the one shown in the figure (a large equilateral triangle made up of small equilateral triangles). The figure shows a figure consisting of 4 levels of triangles.
Write a program that will determine how many triangles there are in total (it is necessary to take into account not only "small" triangles, but in general all triangles — in particular, the triangle in bold, as well as the whole figure, are triangles of interest to us).
Input
Enter one number N — number of levels in the figure (1 ≤ N ≤ 100000).
Imprint
Print the number of triangles in such a figure.
Examples
| # |
Input |
Output |
| 1 |
1 |
1 |
| 2 |
2 |
5 |
| 3 |
4 |
27 |