// Read N from keybird and sum up 1 - N: 1+2+...+N

import java.util.Scanner;

class SumUp_1_N
{
	public static void main(String[] args)
	{
			Scanner input = new Scanner(System.in);

			int sum = 0;

			int N = input.nextInt();

			int count = 1;
			while (count <= N)
			{
				sum += count;
				count ++;
			}

			// debug
			//System.out.println("count = " + count);

			System.out.println("sum = " + sum);

			System.out.println ("\n\n\n");
	}
}