public class RecursiveSum {
    public static void main(String[] args) {

	final int N = Integer.parseInt(args[0]);
	int sum = sum(N);
	System.out.println(sum);

    }

    private static int sum(int n) {
	if (n==0)
	    return 0;
	else
	    return n + sum(n-1);
    }

} // Class RecursiveSum