A. Alex and a Rhombus
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

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.

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.

Examples
Input
1
Output
1
Input
2
Output
5
Input
3
Output
13
Note

Images of rhombus corresponding to the examples are given in the statement.