Given an integer n, find the nth Pentagonal number. First three pentagonal numbers are 1, 5 and 12 (Please see below diagram).The n’th pentagonal number P_{n} is the number of distinct dots in a pattern of dots consisting of the outlines of regular pentagons with sides up to n dots, when the pentagons are overlaid so that they share one vertex.
Pentagonal Number
Example 1:
Input:
n = 1
Output:
1
Explanation:
See the diagram given above.
Example 2:
Input:
n = 2
Output:
5
Explanation:
See the diagram given above.
Example 3:
Input:
n = 3
Output:
12
Explanation:
See the diagram given above.

Your Task:
You don't need to read input or print anything. Your task is to complete the function getNthPentagonalNum() which takes an Integer n as input and returns the answer.

Expected Time Complexity: O(1)
Expected Auxiliary Space: O(1)

Constraints:
1 <= n <= 10^{5}

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