CF1180A.Alex and a Rhombus

普及/提高-

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题目描述

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.

输入格式

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.

输出格式

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

输入输出样例

输入#1
```
1
```
输出#1
```
1
```
输入#2
```
2
```
输出#2
```
5
```
输入#3
```
3
```
输出#3
```
13
```

说明/提示

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

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