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

public class Solution {

    static BigInteger  sumOfGroup(int k) {
        BigInteger term = new BigInteger(Integer.toString(k));
        term = term.multiply(new BigInteger(Integer.toString(k - 1)));
        term = term.add(new BigInteger("1"));
        
        BigInteger sum = new BigInteger("0");
        for (int i = 0; i < k; i++) {
            sum = sum.add(term);
            term = term.add(new BigInteger("2"));
        }
        return sum;
    }

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