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Input

The input contains a single integer a (1 ≤ a ≤ 18257).

Output

Print a single integer output (1 ≤ output ≤ 2·109).

Examples

Input

2


Output

13
import java.io.*;
import java.util.*;

public class p171b
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        long a = sc.nextLong();
        long count = 6*a*(a-1)+1;
        System.out.println(count);
    }
}