백준 8393

import java.util.Scanner;


public class Main8393 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int sum=0;
		for(int i=1; i <= n; i++)
			sum+=i;
		
		System.out.println(sum);

	}

}