import java.util.*;
public class Sum {
	public static void main(String[] args) {
		try(Scanner input =new Scanner(System.in)){
			byte EndNumber=input.nextByte();
			int Goukei=EndNumber*(1+EndNumber)/2;
			System.out.println(Goukei);
		}catch(Exception e){
			e.printStackTrace();
		}
	}
}