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.*;
/*
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 * and open the template in the editor.
 */

/**
 *
 * @author Vishwa Raval
 */
public class TriangularNumber {
    static boolean check(int n){
        if (1<=n && n<=500){
            int sum = 0;
            for (int a=1;sum<=n;a++){
                sum=sum+a;
                if (sum==n){
                    return true;
                }
                
            }
        }
        return false;
    }
    
    public static void main(String[] args) {
        Scanner input=new Scanner(System.in);
        
        int n=input.nextInt();
        
        if (check(n)){
            System.out.println("YES");
        }
        else
            System.out.println("NO");
    }
}
