A. Triangular numberstime limit per test2 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard outputA 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.org/wiki/Triangular_number).Your task is to find out if a given integer is a triangular number.InputThe first line contains the single number n (1 ≤ n ≤ 500) — the given integer.OutputIf the given integer is a triangular number output YES, otherwise output NO.ExamplesInput1OutputYESInput2OutputNOInput3OutputYES
Input1
OutputYES
['brute force', 'math', '*800']