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.io.*;
import java.util.*; 
public class Main{
  
  
  static void chekctri ( int n) 
  { 
    Vector<Integer> v = new Vector<Integer>(); 
    int sum=0;
    for (int i=0;i<=500;i++){
      sum+=i;
      v.add(sum);
    }
    if (v.contains(n))
      System.out.println("YES");
      else
      System.out.println("NO");
  }
  //scanner
  static class FastReader  { 
    BufferedReader br; 
    StringTokenizer st; 
    
    public FastReader()   { 
      br = new BufferedReader(new
                                InputStreamReader(System.in)); 
    } 
    
    String next()   { 
      while (st == null || !st.hasMoreElements()) 
      { 
        try
        { 
          st = new StringTokenizer(br.readLine()); 
        } 
        catch (IOException  e) 
        { 
          e.printStackTrace(); 
        } 
      } 
      return st.nextToken(); 
    } 
    
    int nextInt() 
    { 
      return Integer.parseInt(next()); 
    } 
    
    long nextLong() 
    { 
      return Long.parseLong(next()); 
    } 
    
    double nextDouble() 
    { 
      return Double.parseDouble(next()); 
    } 
    
    String nextLine() 
    { 
      String str = ""; 
      try
      { 
        str = br.readLine(); 
      } 
      catch (IOException e) 
      { 
        e.printStackTrace(); 
      } 
      return str; 
    } 
  }
  // driver
  public static void main(String[] args) throws IOException
  { 
    FastReader s=new FastReader(); 
    int n = s.nextInt(); 
    chekctri(n); 
  } 
}
 	    			 	  		 		 					 	 	