Problem Description

DISTO, a professional photographer, took a photo of black square chips, as shown in the figure below.

However, only the inside of the brown frame is the actual photo. Also, at the spots pointed by the green arrows, the vertices of the chips are touching the edge of the photo, and the photo's sides are bisected.

DISTO thought of compressing the photo into a smaller image data. The compressed image data is represented as an $N \times N$ grid.
The color of each cell in the compressed image data is determined as follows: When the photo is divided into $N \times N$ regions by equally dividing its height and width, only the cells corresponding to regions that are completely black will be black; otherwise, they will be white.

Among the $ N^2 $ cells that make up the compressed image data, how many are black?

Input Format

The input is given from the standard input in the following format.

$ N $

Output Format

Output the number of black cells in the compressed image data.

Sample Input and Output

Sample Input #1

5

Sample Output #1

5

Sample Input #2

10

Sample Output #2

40

Sample Input #3

21

Sample Output #3

181

Notes/Hints

Constraints

• $ N $ is an integer between 2 and 100 inclusive.

Sample Explanation 1

The photo is divided into $5 \times 5$ regions, and the number of regions that are completely black is 5.

Sample Explanation 2

The photo is divided into $10 \times 10$ regions, and the number of regions that are completely black is 40.

Sample Explanation 3

The photo is divided into $21 \times 21$ regions, and the number of regions that are completely black is 181.

见题面 Input 部分

见题面 Output 部分