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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.util.*;
import java.io.*;
public class j {
public static void main(String[] args) throws Exception
{
    Scanner input = new Scanner(System.in);
    PrintWriter out = new PrintWriter(System.out);
    int n = input.nextInt();
    out.println((long)6*n*n-6*n+1);
    out.close();
}
}
