题目描述
Hexagonal numbers are figurate numbers which can be calculated using the formula hn = 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.
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分
样例输入
3
样例输出
15