|Codeforces Round #569 (Div. 2)|
While playing with geometric figures Alex has accidentally invented a concept of a $$$n$$$-th order rhombus in a cell grid.
A $$$1$$$-st order rhombus is just a square $$$1 \times 1$$$ (i.e just a cell).
A $$$n$$$-th order rhombus for all $$$n \geq 2$$$ one obtains from a $$$n-1$$$-th order rhombus adding all cells which have a common side with it to it (look at the picture to understand it better).
Alex asks you to compute the number of cells in a $$$n$$$-th order rhombus.
The first and only input line contains integer $$$n$$$ ($$$1 \leq n \leq 100$$$) — order of a rhombus whose numbers of cells should be computed.
Print exactly one integer — the number of cells in a $$$n$$$-th order rhombus.
Images of rhombus corresponding to the examples are given in the statement.