//
// use a method to do summation 1+2+...+n
//

import java.util.Scanner;
class TestSum
{
	public static void main(String[] args)
	{
		Scanner input = new Scanner(System.in);
		int n = input.nextInt();
		int sum;

		sum = Sum(n);

		System.out.println("Answer is " + sum + "\n\nDone.\n\n");
	}

	//--------------------------
	public static int Sum(int n)
	{	// 1+2+...+n
		int s = 0;
		for(int i=0; i<=n; i++)
			s += i;
		return s;
	}
}