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.util.*;
import java.io.*;

public class Main
{
	public static void main( String[] args )
	{
		Scan scan=new Scan();
		int n=scan.nextInt();
		boolean ans=false;
		for(int i=1;i<=500;i++)
		{
			if(i*(i+1)/2 == n)
			{
				ans=true;
				break;
			}
		}
		System.out.println( ans?"YES":"NO" );
	}
}

class Scan
{
	public BufferedReader br;
	public StringTokenizer st;

	public Scan()
	{
		br = new BufferedReader( new InputStreamReader( System.in ) );
	}

	public boolean hasNext()
	{
		while ( st == null ||  ! st.hasMoreElements() )
		{
			try
			{
				st = new StringTokenizer( br.readLine() );
			}
			catch ( Exception e )
			{
				return false;
			}
		}
		return true;
	}
	public String next()
	{
		if(hasNext())
			return st.nextToken();
		return null;
	}
	public int nextInt()
	{
		if(hasNext())
			return Integer.parseInt(st.nextToken());
		return -1;
	}
}
