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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.awt.*;
import java.awt.geom.*;
import java.io.*;
import java.math.*;
import java.text.*;
import java.util.*;

/*
br = new BufferedReader(new FileReader("input.txt"));
pw = new PrintWriter(new BufferedWriter(new FileWriter("output.txt")));
br = new BufferedReader(new InputStreamReader(System.in));
pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
 */

public class Main {
	private static BufferedReader br;
	private static StringTokenizer st;
	private static PrintWriter pw;

	static int[][] dp;

	static LinkedList<Integer>[] edges;

	static int[] dist;

	public static void main(String[] args) throws IOException	{
		br = new BufferedReader(new InputStreamReader(System.in));
		pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
		int n = readInt();
		long ret = 1;
		for(int i = 2; i <= n; i++)	{
			ret += 12*(i-1);
		}
		pw.println(ret);
		pw.close(); 
	}

	/* NOTEBOOK CODE */

	public static void loadArray(int[][] grid) throws IOException {
		for(int[] a: grid)
			loadArray(a);
	}

	public static void loadArray(int[] in) throws IOException {
		for(int i = 0; i < in.length; i++)
			in[i] = readInt();
	}

	public static void loadArray(long[] in) throws IOException {
		for(int i = 0; i < in.length; i++)
			in[i] = readLong();
	}


	private static long readLong() throws IOException	{
		return Long.parseLong(nextToken());
	}

	private static double readDouble() throws IOException	{
		return Double.parseDouble(nextToken());
	}

	private static int readInt() throws IOException	{
		return Integer.parseInt(nextToken());
	}

	private static String nextToken() throws IOException	{
		while(st == null || !st.hasMoreTokens())	{
			if(!br.ready())	{
				pw.close();
				System.exit(0);
			}
			st = new StringTokenizer(br.readLine().trim());
		}
		return st.nextToken();
	}
}