import java.io.*;
import java.util.*;
public class numGroups {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long k = sc.nextLong();
		long n = k * (k+1)/2;
		long m = (k-1) * k/2;
		System.out.println(n * n - m * m);
	}

}