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. . You can learn more about these numbers from Wikipedia (http:en.wikipedia.orgwikiTriangular_number). Your task is to find out if a given integer is a triangular number.

输入描述:

The first line contains the single number n (1 ≤ n ≤ 500) — the given integer.

输出描述:

If the given integer is a triangular number output YES, otherwise output NO.