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

/**
 *
 * @author takhi
 */
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;


public class Main {


    
    public static void main(String[] args) throws NumberFormatException, IOException {
        

        
                
    BufferedReader r=new BufferedReader(new InputStreamReader(System.in));
        
    






PrintWriter pr=new PrintWriter(System.out);

//StringTokenizer st=new StringTokenizer(r.readLine());


int n=Integer.parseInt(r.readLine());

for(int i=1;i<=100;i++)
{
    int x=(i*(i+1))/2;
    if(x>n)
    {
        pr.println("NO");
        break;
    }
    if(x==n)
    {
        pr.println("YES");
        break;
    }
    
}
pr.flush();
pr.close();
    }}