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.IOException;
import java.io.InputStreamReader;
import java.io.BufferedReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.util.HashSet;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 * @author Zyflair Griffane
 */
public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		PandaScanner in = new PandaScanner(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		A solver = new A();
		solver.solve(1, in, out);
		out.close();
	}
}

class A {
    public void solve(int testNumber, PandaScanner in, PrintWriter out) {
        HashSet<Integer> yes = new HashSet<>();
        for (int i = 0; i < 500; i++) {
            yes.add((i * (i + 1)) >> 1);
        }
        out.println(yes.contains(in.nextInt()) ? "YES" : "NO");
    }
}

class PandaScanner {
    public BufferedReader br;
    public StringTokenizer st;
    public InputStream in;

    public PandaScanner(InputStream in) {
        br = new BufferedReader(new InputStreamReader(this.in = in));
    }

    public String nextLine() {
        try {
            return br.readLine();
        }
        catch (Exception e) {
            return null;
        }
    }

    public String next() {
        if (st == null || !st.hasMoreTokens()) {
            st = new StringTokenizer(nextLine().trim());
            return next();
        }
        return st.nextToken();
    }

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

    }

