import java.util.Scanner;

class Main {
    public static void main(String args[]) {
        Scanner scanner = new Scanner(System.in);
        String input = scanner.nextLine();
        int num = Integer.parseInt(input);
        int sum = 0;

        for(int i = 1; i <= num; i++){
            sum += i;
        }
        System.out.println(sum);
        scanner.close();
    }
}