HDU1001

import java.util.Scanner;

public class HDU1001 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = 0;
        while (sc.hasNext()) {
            int sum = 0;
            n = sc.nextInt();
            for (int i = 1; i <= n; i++) {
                sum += i;
            }
            //sum=(int)((n+1)*n/2);
            System.out.println(sum + "\n\n");
            // System.out.println();
        }
    }
}