/**
 * Created by iyasuwatts on 10/17/17.
 */
import java.util.*;
public class Main {

    public static void main(String[] args){
        int sumOfNumbers = 0;
        
        Scanner in = new Scanner(System.in);
        System.out.print("Gimme number pls!\n");
        int n = in.nextInt();
        for (int i = 1; i <= n; i++) {
            sumOfNumbers += i;
        }
        System.out.println(sumOfNumbers);
    }
}