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 kk = BigInteger.valueOf(k).multiply(BigInteger.valueOf(k + 1)).subtract(BigInteger.valueOf(1L));
        BigInteger last =  kk;
        BigInteger sum = BigInteger.valueOf(0L);
        BigInteger two = BigInteger.valueOf(2L);

        for (; k > 0; k--) {
            sum = sum.add(last);
            last = last.subtract(two);
        }

        return sum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int k = in.nextInt();

        System.out.println(sumOfGroup(k));
        in.close();
    }
}