import java.util.*;
public class Sum2 {

    public static void main(String[] args) {
        Scanner sc= new Scanner(System.in);
        int x=sc.nextInt();
        int sum=0;
        if(x<=0){
            for(int i=x;i<=1;i++){
            sum+=i;
        }
            System.out.println(sum);
        }
        else if(x<10000){
            for(int i=1;i<=x;i++){
                sum+=i;
            }
            System.out.println(sum);
        }

    }
}