Sum 2#9971

Sum 2

1 second
64 megabytes
Very easy

Calculate the sum of the first terms in the sequence: 2, 5, 8, 11, 14, \ldots

Input

A natural number , where 1 \leq n \leq 100.

Output

Output a single integer — the sum of the first terms of the sequence.

Examples

Example 1

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