import java.util.Scanner;
import java.io.*;

public class HelloWorld {

    public static void main(String args[]) {

        int a = 0;
        int total = 0;
        Scanner input = new Scanner(System.in);
        a = input.nextInt();


            total = convertFunc(a);
            System.out.println(total);
    }

        public static int convertFunc(int n){

        int sum = 0;
        if(n > 0 && n <= 10000 )
        {
            for(int i = 1 ; i <= n ; i++ )
            {
                sum += i;
            }
        }
        else
        {
            for(int i = 1 ; i >= n ; i--)
            {
                sum += i;
            }
        }
        return sum;
    }
}