Sum

Sum

import java.util.Scanner;	

class Sum {
	public static void main(String [] args) {

		Scanner input = new Scanner(System.in);

		int n, x, absn, sum; 

		x = 0;

		n = input.nextInt();
		absn = Math.abs(n);

		if (absn<10000){
			
			if(n>=0){

			while(n>0){

			sum = n;
			n = n - 1;
			x = x + sum;
			}

		System.out.println(x);

		}

		else if(n<0){

			while(n<=1){

			sum = n;
			n = n + 1;
			x = x + sum;
			}
		System.out.println(x);

		}


		else {
			System.out.println(0);
		}
	}
}
}