# The Chess Board

You are given a square grid consisting of $n×n$ black and white small squares. This grid can also be represented as a chess board of $kn $ rows and $kn $ columns, where each cell consists of $k×k$ small squares of one color. You need to calculate the number of white squares in this grid.

Example of the board for $n=6$ and $k=3$. As you can see, there are $18$ white squares on it. The lighter color is white and the other is black.

Please note that the cell in the first row and the first column is white.

## Input

The first line contains two integers $n$ and $k$ $(1≤n,k≤100)$ — the size of a grid and each cell respectively. It is guaranteed that $n$ is divisible by $k$.

## Output

You have to output a single line containing one integer: the number of white squares on a grid.

## Examples

## Scoring

($5$ points): $n=1$;

($10$ points): $k=1$;

($15$ points): $kn $ is even;

($20$ points): no additional constraints.