<image>

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.PrintWriter;
import java.util.Scanner;

public class First {
	static Scanner in; static int next() throws Exception {return in.nextInt();};
//	static StreamTokenizer in; static int next() throws Exception {in.nextToken(); return (int) in.nval;}
//	static BufferedReader in;
	static PrintWriter out;

	public static void main(String[] args) throws Exception {
		in = new Scanner(System.in);
//		in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
//		in = new BufferedReader(new InputStreamReader(System.in));
		out = new PrintWriter(System.out);

        int n = next();

        int res = 1;

        for (int i = 0;i < n;i++) res += i*12;
        out.println(res);

        out.println();
		out.close();
	}
}