package practice;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Sum {


    public static void main(String[] args) {
        // TODO Auto-generated method stub
        //Scanner sc = new Scanner (System.in);
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int x = 0;
        int sum = 0;
        try {
            x = (int)br.read();
            System.out.println("x" +x);
            if(x >0){
                for(int i =1; i <= x ;i++){
                    sum = sum +i;
                }
                }
                else {
                    for(int i =x; i <=1 ;i++){
                        sum = sum +i;
                    }
                }

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }




        System.out.println(sum);
    }

}