The K-th Pentagonal Number

Difficulty: 1100 2000 ms 128 MB

math

Print the K-th of the pentagonal numbers (1, 5, 12, 22, ...) (1-indexed).

Input: one integer K.

Output: the K-th such number.

Constraints:

• 1 ≤ K ≤ 100000000

Sample Tests

3

12

1

1

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