// Sum of first n natural number
import java.util.*;
public class SumOfNaturalNumber {
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int sum = 0;

        for(int i = 1; i <= n; i++){
            sum = sum + i;
        }
        System.out.println(sum);
    }
    
}