[Codeforces] Alex and a Rhombus

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 nn-th order rhombus in a cell grid.

A 11-st order rhombus is just a square 1×11×1 (i.e just a cell).

A nn-th order rhombus for all n≥2n≥2 one obtains from a n−1n−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 nn-th order rhombus.

Input

The first and only input line contains integer nn (1≤n≤1001≤n≤100) — order of a rhombus whose numbers of cells should be computed.

Output

Print exactly one integer — the number of cells in a nn-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.

算格子數

就是等差數列 1 + 3 + 5 + ....

最後一塊 last = n * 2 -1; 這個會重複

class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(Solution.Compute(Convert.ToInt32(Console.ReadLine())));
        }
    }

    class Solution
    {
        public static int Compute(int n)
        {
            int last = n *  - ;
            return ( + last) * n - last;
        }
    }