Alex and a Rhombus

给你一个整数$n$，你需要求出从$1\times 1$开始扩展$n-1$次的格子数量。 每一次扩展，所有与当前格子有边相邻的格子都会被扩展进答案里。比如$n\le 3$的情形如下面这张图： 

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.

1

1

2

5

3

13

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