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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;
import java.util.StringTokenizer;

public class A47 {
	BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
	StringTokenizer st = null;

	private void solution() throws IOException {
		double n=nextInt();
		 for (int i=1; i<=n; i++) {
		        double t = i*(i+1)/2.0;
		        if ( t == n) { System.out.println("YES"); return;  }
		        else if (t>n) { System.out.println("NO"); return; }
		    }
		  }

	String nextToken() throws IOException {
		if (st == null || !st.hasMoreTokens()) {
			st = new StringTokenizer(bf.readLine());
		}
		return st.nextToken();
	}

	int nextInt() throws IOException {
		return Integer.parseInt(nextToken());
	}

	long nextLong() throws IOException {
		return Long.parseLong(nextToken());
	}

	double nextDouble() throws IOException {
		return Double.parseDouble(nextToken());
	}

	public static void main(String args[]) throws IOException {
		new A47().solution();
	}
}