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Time limit 2000/4000/4000/4000 ms. Memory limit 65000/65000/65000/65000 Kb.
Triangular Numbers
Shqip
Square Numbers are the numbers which can be represented as a square; like 4, 16 or 25.
Triangular Numbers are similar to square numbers but they form a triangle.
Write a program that is going to accept an integer number and decide if the number is a triangular number or not.
Input specification
There will be just one integer number n where 1 ≤ n ≤ 1 billion.
Output specification
Print out "YES" if the given number is a triangular number. "NO", otherwise.
Sample Input:
5
Sample Output:
NO
Sample Input:
21
Sample Output:
YES
Для отправки решений необходимо выполнить вход.
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