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.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.*;
public class C {
    static class FastScanner {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer("");

        String next() {
            while (!st.hasMoreTokens())
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            return st.nextToken();
        }

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

        int[] nextArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++) a[i] = nextInt();
            return a;
        }

        long nextLong() {
            return Long.parseLong(next());
        }
    }
    static class FastWriter extends PrintWriter {
        FastWriter() {
            super(System.out);
        }

        void println(int[] array) {
            for (int i = 0; i < array.length; i++) {
                print(array[i] + " ");
            }
            println();
        }

        void println(long[] array) {
            for (int i = 0; i < array.length; i++) {
                print(array[i] + " ");
            }
            println();
        }
    }
    public static void main(String[] args) {
        // Yo bitch !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
        FastScanner in = new FastScanner();
        FastWriter out = new FastWriter();
//        int t=in.nextInt();
//        while(t-->0){
//            int n=in.nextInt();
//            int[] ar=in.nextArray(n);
//        }
        int n=in.nextInt();
        for (int i = 1; i <= n; i++) {
            if(i*(i+1)/2==n){
                System.out.println("YES");
                return;
            }
        }
        System.out.println("NO");
        out.close();
    }
}