Read problem statements in [Mandarin Chinese] and [Bengali].

Given n (n is even), determine the number of black cells in an $n \times n$ chessboard.

------ Input Format ------

The only line of the input contains a single integer n.

------ Output Format ------

Output the number of black cells in an $n \times n$ chessboard.

------ Constraints ------

$2 ≤ n ≤ 100$
$n$ is even

----- Sample Input 1 ------
8
----- Sample Output 1 ------
32
----- explanation 1 ------

There are $32$ black cells and $32$ white cells in an $8 \times 8$ chessboard. So the answer is $32$.

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