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

public class Solution {
    static BigInteger sumOfGroup(long k) {
        // Return the sum of the elements of the k'th group.
        //BigInteger start = BigInteger.valueOf(k*(k-1)+1);
        BigInteger start = BigInteger.valueOf(k);
        start = start.multiply(start.subtract(BigInteger.valueOf(1))).add(BigInteger.valueOf(1));
        BigInteger sum=BigInteger.valueOf(0);
        BigInteger d=BigInteger.valueOf(2);
        BigInteger n=BigInteger.valueOf(k);
        sum=n.multiply(start.multiply(BigInteger.valueOf(2)).add(n.subtract(BigInteger.valueOf(1)).multiply(d))).divide(BigInteger.valueOf(2));
        
        return sum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long k = in.nextLong();
        BigInteger answer = sumOfGroup(k);
        System.out.println(answer);
        in.close();
    }
}