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.BufferedReader;
//import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
//import java.io.FileReader;
//import java.io.FileWriter;
//import java.lang.StringBuilder;
import java.util.StringTokenizer;
//import java.lang.Comparable;
//import java.util.Arrays;
//import java.util.HashMap;
//import java.util.ArrayList;

public class TriangularNumbers {
    
    //static BufferedReader in = new BufferedReader(new FileReader("input.txt"));
    //static PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("output.txt")));
    static BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    static PrintWriter out = new PrintWriter(System.out);
    
    public static void main(String[] args) throws IOException {
        int n = 0;
        int r = Integer.parseInt(in.readLine()) * 2;
        for(int i = 1; n < r; i++) {
            n += (2 * i);
        }
        if(n == r) {
            out.print("YES");
        } else {
            out.print("NO");
        }
        out.close();
    }
}