import java.math.BigInteger;
import java.util.Locale;
import java.util.Scanner;

public class NumberGroups {

    public static void main(String[] args) {
        try(Scanner in = new Scanner(System.in)){
            in.useLocale(Locale.ENGLISH);
            int k = in.nextInt();
            System.out.println(solve(k));
        }
    }

    private static String solve(int k) {
        BigInteger ks = BigInteger.valueOf(k);
        BigInteger kplusone = ks.add(BigInteger.ONE);
        BigInteger t1 = kplusone.multiply(ks);
        BigInteger t2 = t1.divide(BigInteger.valueOf(2));
        BigInteger t2sq = t2.multiply(t2);

        BigInteger kminusone = ks.subtract(BigInteger.ONE);
        BigInteger t1a = kminusone.multiply(ks);
        BigInteger t2a = t1a.divide(BigInteger.valueOf(2));
        BigInteger t2asq = t2a.multiply(t2a);

        BigInteger result = t2sq.subtract(t2asq);
        return result.toString();
    }
}