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A. Hexagonal numbers
time limit per test
2 seconds
memory limit per test
64 megabytes
input
standard input
output
standard output

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
2
Output
6
Input
5
Output
45