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.*;
import java.math.*;

public class A implements Runnable {

	void solve() {
		int n = nextInt();
		for (int i = 0; i <= n; i++) {
			if (i * (i + 1) / 2 == n) {
				out.println("YES");
				return;
			}
		}
		out.println("NO");
	}

	FastScanner sc;
	PrintWriter out;

	public void run() {
		Locale.setDefault(Locale.US);
		try {
			sc = new FastScanner(System.in);
			out = new PrintWriter(System.out);
			solve();
			sc.close();
			out.close();
		} catch (Throwable e) {
			e.printStackTrace();
			System.exit(1);
		}
	}

	int nextInt() {
		return sc.nextInt();
	}

	String nextToken() {
		return sc.nextToken();
	}

	long nextLong() {
		return sc.nextLong();
	}

	double nextDouble() {
		return sc.nextDouble();
	}

	BigInteger nextBigInteger() {
		return sc.nextBigInteger();
	}

	class FastScanner extends BufferedReader {
		StringTokenizer st;
		boolean eof;
		String buf;
		String curLine;
		boolean createST;

		public FastScanner(String fileName) throws FileNotFoundException {
			this(fileName, true);
		}

		public FastScanner(String fileName, boolean createST)
				throws FileNotFoundException {
			super(new FileReader(fileName));
			this.createST = createST;
			nextToken();
		}

		public FastScanner(InputStream stream) {
			this(stream, true);
		}

		public FastScanner(InputStream stream, boolean createST) {
			super(new InputStreamReader(stream));
			this.createST = createST;
			nextToken();
		}

		String nextLine() {
			String ret = curLine;
			if (createST) {
				st = null;
			}
			nextToken();
			return ret;
		}

		String nextToken() {
			if (!createST) {
				try {
					curLine = readLine();
				} catch (Exception e) {
					eof = true;
				}
				return null;
			}
			while (st == null || !st.hasMoreTokens()) {
				try {
					curLine = readLine();
					st = new StringTokenizer(curLine);
				} catch (Exception e) {
					eof = true;
					break;
				}
			}
			String ret = buf;
			buf = eof ? "-1" : st.nextToken();
			return ret;
		}

		int nextInt() {
			return Integer.parseInt(nextToken());
		}

		long nextLong() {
			return Long.parseLong(nextToken());
		}

		double nextDouble() {
			return Double.parseDouble(nextToken());
		}

		BigInteger nextBigInteger() {
			return new BigInteger(nextToken());
		}

		public void close() {
			try {
				buf = null;
				st = null;
				curLine = null;
				super.close();
			} catch (Exception e) {

			}
		}

		boolean isEOF() {
			return eof;
		}
	}

	public static void main(String[] args) {
		new A().run();
	}
}