<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.InputStreamReader;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.InputStream;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;
/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 * @author Erasyl Abenov
 * 
 * 
 */
public class Main {
    public static void main(String[] args) throws IOException {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
            try (PrintWriter out = new PrintWriter(outputStream)) {
                TaskB solver = new TaskB();
                solver.solve(1, in, out);
            }
    }
}
class TaskB {
    public void solve(int testNumber, InputReader in, PrintWriter out) throws IOException{
        int a = in.nextInt();
        out.println(1L*6*a*(a - 1) + 1);
    }
}
class InputReader {
    private final BufferedReader reader;
    private StringTokenizer tokenizer;
    public InputReader(InputStream stream) {
        reader = new BufferedReader(new InputStreamReader(stream));
        tokenizer = null;
    }
      
    public String nextLine() {
        try {
            return reader.readLine();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
      
    public String next() {
        while (tokenizer == null || !tokenizer.hasMoreTokens()) {
            tokenizer = new StringTokenizer(nextLine());
        }
        return tokenizer.nextToken();
    }
      
    public int nextInt() {
        return Integer.parseInt(next());
    }
    public BigInteger nextBigInteger(){
        return new BigInteger(next());
    }
    public long nextLong() {
        return Long.parseLong(next());
    }
    public double nextDouble() {
        return Double.parseDouble(next());
    }
}