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 upperBound = BigInteger.valueOf(k).multiply(BigInteger.valueOf(k+1));
        BigInteger lowerBound = BigInteger.valueOf(k-1).multiply(BigInteger.valueOf(k));
        BigInteger two = BigInteger.valueOf(2);
        
        //System.out.println("lowerBound: "+lowerBound);
        //System.out.println("upperBound: "+upperBound);
        
        if (lowerBound.mod(two) == BigInteger.ZERO)
            lowerBound = lowerBound.add(BigInteger.ONE);
        if (upperBound.mod(two) == BigInteger.ZERO)
            upperBound = upperBound.subtract(BigInteger.ONE);
        
        //System.out.println("lowerBound: "+lowerBound);
        //System.out.println("upperBound: "+upperBound);
        
        BigInteger n = ((upperBound.subtract(lowerBound)).divide(two)).add(BigInteger.ONE);
        BigInteger sum = ((upperBound.add(lowerBound)).divide(two)).multiply(n);
        
        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();
    }
}