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

public class Solution {

    static void sumOfGroup(int k) {
        BigInteger a,b,c, res, res1;
        a = BigInteger.valueOf(k);
        b = BigInteger.valueOf(k+1);
        c = BigInteger.valueOf(k-1);
        res = a.multiply(b).divide(BigInteger.valueOf(2));
        res1 = a.multiply(c).divide(BigInteger.valueOf(2));
        res = res.multiply(res);
        res1 = res1.multiply(res1);
 
        System.out.println(res.subtract(res1).toString());
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int k = in.nextInt();
        sumOfGroup(k);
        in.close();
    }
}