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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 Main {

    public Scanner sc;
    
    public void run() {
        int n = sc.nextInt();
        System.out.println(1+6*n*(n-1));
    }
    
    public static void main(String[] args) {
        Main main = new Main();
        try { main.sc = new Scanner(new FileInputStream("test.in")); }
        catch (FileNotFoundException e) { main.sc = new Scanner(System.in); }
        main.run();
    }

}