import java.util.Scanner;


public class r1068 {
    public static void main(String[] args) {
        Scanner rr = new Scanner(System.in);
        int n = rr.nextInt();
        int w=0;
        if ((n>=1)&&(n<=10000)) {
            for(int i=1; i<=n;i++){
                w=w+i;
            }
            System.out.println(w);
        }
        if ((n<=1)&&(n>=-10000)) {
            for (int i=1; i<=Math.abs(n); i++){
                w=w+(-i);
            }
            System.out.println(w+1);
        }
    }
}

Edited by author 13.04.2017 18:52

Test input: 1

Edited by author 13.04.2017 19:44