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

public class Solution {

    static long sumOfGroup(int k) {
        // Return the sum of the elements of the k'th group.

        BigInteger kValue = BigInteger.valueOf(k);
        BigInteger kValueMinus1 = BigInteger.valueOf(k - 1);
        BigInteger leftRange = kValue.multiply(kValueMinus1);

        BigInteger currentNumber = leftRange.add(BigInteger.valueOf(1));
        BigInteger sum = BigInteger.ZERO;

        for(int number = 0; number < k; number++) {
            sum = sum.add(currentNumber);
            currentNumber = currentNumber.add(BigInteger.valueOf(2));
        }

        return sum.longValue();
    }

    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();
    }
}