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
//package acm;

import java.util.*;


/* http://codeforces.com/problemset/problem/47/A  */
public class Main {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        Vector<Integer> v = new Vector<>();
        for (int i = 1; true; i++) {
            if (i * (i + 1) / 2 > 500) {
                break;
            }
            v.addElement(i * (i + 1) / 2);

        }
        
        int n = in.nextInt();
        if(v.contains(n))
            System.out.println("YES");
        else
            System.out.println("NO");

    }

}
