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.InputStreamReader;
import java.io.PrintWriter;
import java.io.StreamTokenizer;
import java.util.ArrayDeque;
import java.util.HashMap;
import java.util.HashSet;

public class Main {
    private static StreamTokenizer in;
    private static PrintWriter out;
    private static BufferedReader inB;
    
    private static int nextInt() throws Exception{
        in.nextToken();
        return (int)in.nval;
    }
    
    private static String nextString() throws Exception{
        in.nextToken();
        return in.sval;
    }
    
    static{
        inB = new BufferedReader(new InputStreamReader(System.in));
        in = new StreamTokenizer(inB);
        out = new PrintWriter(System.out);
    }
    
    public static void main(String[] args)throws Exception{
//      int[] mas = new int[500];
        HashSet<Integer> hs = new HashSet<Integer>();
        
        
        for(int i = 1; i<=500; i++) {
            hs.add((i*(i+1)) / 2);
        }
        
        int n = nextInt();
        
        out.println(hs.contains(n) ? "YES" : "NO");
        
        out.flush();
    }
}
