import java.util.Arrays;
import java.util.Scanner;
public class calcu{
    public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        int sum = 0;
        int i;
        int n = stdIn.nextInt();
        for(i = 1; i <= n; i++){
            sum += i;
        }
        System.out.println(sum);
        stdIn.close();
    }
}