Alex and a Rhombus

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 × 1 (i.e just a cell).

A n-th order rhombus for all n ≥ 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 ≤ n ≤ 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.

inputFormat

Input

The first and only input line contains integer n (1 ≤ n ≤ 100) — order of a rhombus whose numbers of cells should be computed.

outputFormat

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.

样例

3

13

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