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

public class Solution {

    static BigInteger sumOfGroup(int k) {
        // Return the sum of the elements of the k'th group.
        BigInteger j = BigInteger.valueOf(k);
        j = j.multiply(BigInteger.valueOf(k - 1));
        j = j.add(BigInteger.valueOf(1));
        BigInteger start = j;
        BigInteger sum = j;
        
        for (int i = 1; i < k; i++) {
            sum = sum.add(start.add(BigInteger.valueOf(i).multiply(BigInteger.valueOf(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();
    }
}