10498: ABC108 —— A - Pair
[Creator : ]
Description
Find the number of ways to choose a pair of an even number and an odd number from the positive integers between $1$ and $K$ (inclusive). The order does not matter.
Input
Input is given from Standard Input in the following format:
```
$K$
```
```
$K$
```
Output
Print the number of ways to choose a pair of an even number and an odd number from the positive integers between $1$ and $K$ (inclusive).
Constraints
- $2\leq K\leq 100$
- $K$ is an integer.
- $K$ is an integer.
Sample 1 Input
3
Sample 1 Output
2
Two pairs can be chosen: (2,1) and (2,3).
Sample 2 Input
6
Sample 2 Output
9
Sample 3 Input
11
Sample 3 Output
30
50
625