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;
mt19937_64 rang(
    chrono::high_resolution_clock::now().time_since_epoch().count());
const int M = 1e9 + 7;
long long power(long long x, long long y) {
  long long v = 1;
  while (y > 0) {
    if (y & 1) v = v * x;
    y = y >> 1;
    x = x * x;
  }
  return v;
}
bool isPowerOfTwo(long long x) { return x && (!(x & (x - 1))); }
long long ceil(long long a, long long b) { return (a + b - 1) / b; }
void init() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
}
void solve() {
  long long n;
  cin >> n;
  set<int> st;
  for (int i = 1; i < 501; i++) {
    int tem = i * (i + 1) / 2;
    st.insert(tem);
  }
  if (st.find(n) != st.end()) {
    cout << "YES"
         << "\n";
  } else {
    cout << "NO"
         << "\n";
  }
}
int main() {
  init();
  long long test = 1;
  while (test--) {
    solve();
  }
  return 0;
}
