Statement

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.

Format

Input

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.

Output

Print exactly one integer — the number of cells in a $n$ -th order rhombus.

Sample

1

1

2

5

3

13