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

/**
 *
 * @author CSC Mohammad Hasan
 */
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int res=s.nextInt();
        
        if(res==1||res==3||res==6||res==10||res==15||res==21||res==28||res==36||res==45||res==55||res==66||res==78||res==91||res==105||res==120||res==136||res==153||res==171||res==190||res==210||res==231||res==253||res==276||res==300||res==325||res==351||res==378||res==406||res==435||res==465||res==496||res==528){
            System.out.println("YES");
        }
        else
            System.out.println("NO");
       
    }

}
