A. Hexagonal Numbers
time limit per test
2 seconds
memory limit per test
256 megabytes
input
stdin
output
stdout

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.

Examples
Input
3
Output
15
Input
6
Output
66