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 odds=BigInteger.valueOf(k).multiply(BigInteger.valueOf(k-1)).add(BigInteger.valueOf(1));
        BigInteger odde=BigInteger.valueOf(1+k).multiply(BigInteger.valueOf(k)).subtract(BigInteger.valueOf(1));
        return (odds.add(odde)).multiply(new BigInteger(k+"")).divide(new BigInteger("2")).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();
    }
}