#include <bits/stdc++.h>
using namespace std;

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

Construct a cpp code solution to the problem outlined:

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 <bits/stdc++.h>
using namespace std;

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