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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 * and open the template in the editor.
 */
import java.util.Scanner;

/**
 *
 * @author yashvi_1902
 */

public class triangularNumbers {
    
  static boolean isTriangularNum(int n){
      int sum=0;
      if (n<0){
          return false;
      }
      
      for(int i=0;sum<=n;i++)
      {
         sum += i;
         if(sum==n)
              return true;
      
      }
      return false;
  }   
   
    public static void main(String[] args) {
       Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        if(isTriangularNum(n)){
            System.out.println("YES");
        }
        else{
            System.out.println("NO");
        }
        
            
            
   }
}
