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 CF44A {
	
	private static BufferedReader	br;
	private static StringTokenizer 	st;
	private static PrintWriter 		pw;
	// private static Timer t = new Timer();
	
	public CF44A() throws IOException {
		br = new BufferedReader(new InputStreamReader(System.in));
		pw = new PrintWriter(System.out);
	}
	
	String next() throws IOException {
        while (st == null || !st.hasMoreElements())
            st = new StringTokenizer(br.readLine());
        return st.nextToken();
    }

    boolean hasNext() {
        if (st != null && st.hasMoreElements())
            return true;

        try {
            while (st == null || !st.hasMoreElements())
                st = new StringTokenizer(br.readLine());
        }
        catch (Exception e) {
            return false;
        }

        return true;
    }

    String nextLine() throws IOException {
        return br.readLine();
    }

    int nextInt() throws IOException {
        return Integer.parseInt(next());
    }

    long nextLong() throws IOException {
        return Long.parseLong(next());
    }

	void solve() throws IOException {
		int n = nextInt();
		ArrayList<Integer> list = new ArrayList<>();
		for(int i = 0; i <= 500; i++) {
			list.add(i*(i+1)/2);
		}
		if(list.contains(n))
			pw.println("YES");
		else
			pw.println("NO");
		pw.flush();
	}
		
	public static void main(String[] args) throws IOException{
		 new CF44A().solve();
	 }
}









