import java.util.*; class Sum{ public int Cal(int s){ int gokei = 0; for(int i=1;i<=s;i++){ gokei = gokei + i; } return gokei; } } public class Main{ public static void main(String args[]){ Scanner sc = new Scanner(System.in); int N = sc.nextInt(); Sum sm = new Sum(); int sum = sm.Cal(N); System.out.println(sum); } }