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
#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
const long long inf = 1e18;
const char nl = '\n';
void CP() { ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0); }
bool isTriangular(int num) {
  if (num < 0) return false;
  int sum = 0;
  for (int n = 1; n < (num + 1); ++n) {
    sum = sum + n;
    if (!(sum ^ num)) return true;
  }
  return false;
}
void solve() {
  int n;
  cin >> n;
  if (isTriangular(n))
    cout << "YES";
  else
    cout << "NO";
}
int main() {
  CP();
  solve();
  return 0;
}
