CF162A.Pentagonal numbers

传统题 时间 2000 ms 内存 256 MiB 5 尝试 1 已通过 1 标签

Pentagonal numbers

Pentagonal numbers are figurate numbers which can be calculated using the formula p**n = (3n2 - n) / 2 (always integer). You are given n; calculate n-th pentagonal number.

Input

The only line of input contains an integer n (1 ≤ n ≤ 100).

Output

Output the n-th pentagonal number.

Samples

2
5
5
35

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