import java.util.*;
         
class Main{
    public static void main(String[] args) {
        
        try(Scanner sc = new Scanner(System.in)){

            int in = Integer.parseInt(sc.next());
            int sum = 0;

            for(int i = 0; i < in + 1; i++){
                sum += i;
            }

            System.out.println(sum);

        }catch(Exception e){
            e.printStackTrace();
        }        
    }
}