#include"iostream"
using namespace std;

int main()
{
	int n;
	cin >> n;
	cout << (n / 2)*(n - n / 2) << endl;
}
### Prompt

Please provide a cpp coded solution to the problem described below:

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.

Constraints

* 2\leq K\leq 100
* K is an integer.

Input

Input is given from Standard Input in the following format:


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).

Examples

Input

3


Output

2


Input

6


Output

9


Input

11


Output

30


Input

50


Output

625

### Response

```cpp
#include"iostream"
using namespace std;

int main()
{
	int n;
	cin >> n;
	cout << (n / 2)*(n - n / 2) << endl;
}
```