import java.util.Scanner;
class Wandbox
{
    public static void main(String[] args)
    {
    	Scanner sc = new Scanner(System.in);
    	int num = sc.nextInt();
    	int ans = 0;
    	for (int i = 1; i <= num; i++) {
    		ans += i;
    	} 
        System.out.println(ans);
    }
}