A triangular number is the number of dots in an equilateral triangle uniformly filled with dots. For example, three dots can be arranged in a triangle; thus three is a triangular number. The n-th triangular number is the number of dots in a triangle with n dots on a side. <image>. You can learn more about these numbers from Wikipedia (http://en.wikipedia.org/wiki/Triangular_number).

Your task is to find out if a given integer is a triangular number.

Input

The first line contains the single number n (1 ≤ n ≤ 500) — the given integer.

Output

If the given integer is a triangular number output YES, otherwise output NO.

Examples

Input

1


Output

YES


Input

2


Output

NO


Input

3


Output

YES
import java.io.PrintWriter;
import java.util.Scanner;
import java.util.Vector;

public class Solution {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);

		int n = in.nextInt();

		int cur = 0;
		Vector<Integer> v = new Vector<Integer>();
		int i = 1;

		while (cur <= 500) {
			v.add(cur + i);
			cur += i;
			i++;
		}

		boolean yes = false;

		for (Integer val : v) {
			if (n == val)
				yes = true;
		}

		out.print(yes ? "YES" : "NO");

		out.close();
	}
}
