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
/******************************************************************************

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Write your code in this editor and press "Run" button to execute it.

*******************************************************************************/
import java.util.Scanner;
public class Main
{
	public static void main(String[] args) 
	{
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		int a=1;
		int b=2;
		int x=0;
		
		while(b<=2*n)
		{
		    if(a*b==2*n)
		    {
		        x=1;
		         System.out.println("YES");
		         break;
		    }
		    //System.out.println(a);
		    a++;
		    b++;
		    
		}
		if(x==0){
		    System.out.println("NO");
		}
	}
}
