import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static long sumOfGroup(long k) {
        long firstNumber = (1 + k * (k - 1) / 2) * 2 - 1;
        
        long sum = 0;
        for (int i = 0; i < k; ++i)
        {
            sum += firstNumber;
            firstNumber += 2;
        }
        
        return sum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int k = in.nextInt();
        long answer = sumOfGroup(k);
        System.out.println(answer);
        in.close();
    }
}