A. Pentagonal numbers
time limit per test
3 seconds
memory limit per test
256 megabytes
input
stdin
output
stdout

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.

Examples
Input
2
Output
5
Input
5
Output
35