CF188A.Hexagonal Numbers

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

Hexagonal Numbers

Hexagonal numbers are figurate numbers which can be calculated using the formula h**n = 2n2 - n. You are given n; calculate n-th hexagonal number.

Input

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

Output

Output the n-th hexagonal number.

Samples

3
15
6
66

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