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 r= (BigInteger.valueOf(k-1).multiply(BigInteger.valueOf(k))).divide(BigInteger.valueOf(2));
            BigInteger s= (BigInteger.valueOf(k).multiply(BigInteger.valueOf(k+1))).divide(BigInteger.valueOf(2));
        BigInteger sumF= r.multiply(r);
        BigInteger sumL= s.multiply(s);
            
     return sumL.subtract(sumF); 
        
    }

    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();
    }
}