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

public class Solution {
	static BigInteger one = BigInteger.ONE;
	static BigInteger two = one.add(one);

    static BigInteger sumOfGroup(int k) {
        BigInteger bigK = new BigInteger("" + k);
        //BigInteger bigKplus1 = bigK.add(one);
        BigInteger bigKminus1 = bigK.subtract(one);
        BigInteger num1 = getSum(bigK).subtract(one);
        BigInteger sum1 = getSum(num1);
        BigInteger num2 = getSum(bigKminus1).subtract(one);
        BigInteger sum2 = getSum(num2);
        return ((sum1.subtract(sum2)).multiply(two)).add(bigK);
        // Return the sum of the elements of the k'th group.
    }
    
    static BigInteger getSum(BigInteger k) {
    	BigInteger k1 = k.add(one);
    	return (k.multiply(k1)).divide(two);
    }

    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();
    }

}