P300845 - CF162A. Pentagonal numbers - SSOJ - 省实信息奥赛评测系统

Memory Limit：256 MB Time Limit：3 S

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A. Pentagonal numberstime limit per test3 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard output

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.

ExamplesInput

Output

Input

Output

VK Cup 2012 Wild-card Round 1 - implementation - *1100

300845: CF162A. Pentagonal numbers

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