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Contests > "Informatics Stars" Online Contests - 2011-2014 > problem:


2012-12-20. 50574 - Triangular Numbers

"Informatics Stars" Online Contests - 2011-2014

Start: Oct.20.2012 at 10:00:00 AM
Finish: Oct.20.2012 at 03:00:00 PM
The contest is finished!
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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


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