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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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
//package b;

import java.util.Scanner;

/**
 *
 * @author Usuario
 */
public class B {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        Scanner s = new Scanner(System.in);
        int n = Integer.valueOf(s.nextLine());
        
        int cont = 0;
        int i = 1;
        boolean es = false;
        while(cont<=n){
            cont += i;
            i++;
            if(cont == n){
                es = true;
            }
        }
        if(es)
            System.out.println("YES");
        else
            System.out.println("NO");
    }
    
}
