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.Scanner;

public class MyTask{
	
	public static void main(String args[]){
		Solver s = new Solver();
		s.solve();
	}
}

class Solver{
	
	public void solve(){
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt();
		
		boolean tr[] = new boolean[501];
		int n=1;
		while (true){
			int k = n*(n+1)/2;
			if (k>500)
				break;
			tr[k]=true;
			n++;
		}
		
		System.out.print((tr[x])?"YES":"NO");
	}
}