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A. Alex and a Rhombus

time limit per test

1 secondmemory limit per test

256 megabytesinput

standard inputoutput

standard outputWhile 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.

Codeforces (c) Copyright 2010-2019 Mike Mirzayanov

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