题目描述
Pentagonal numbers are figurate numbers which can be calculated using the formula pn = (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.
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分
样例输入
2
样例输出
5