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 K = new BigInteger(Integer.toString(k));
        
        BigInteger a= (K.multiply(K.subtract(new BigInteger("1")))).add(new BigInteger("1"));
        BigInteger l= (K.multiply(K.add(new BigInteger("1")))).subtract(new BigInteger("1"));
        //System.out.println(a);
        //System.out.println(l);
        BigInteger sum=(K.multiply(a.add(l))).divide(new BigInteger("2"));
        //System.out.println(sum);
        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);
        in.close();
    }
}