Hexagonal Numbers

Time Limit: 2 seconds

Memory Limit: 256 megabytes

Description

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.

Sample Input

Input
3
Output
15
Input
6
Output
66

Sample Output

None

Hint

None

Source

None

提交代码