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

int main() {
  int K;
  cin >> K;
  cout << K/2 * (K/2 + K % 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 <bits/stdc++.h>
using namespace std;

int main() {
  int K;
  cin >> K;
  cout << K/2 * (K/2 + K % 2) << endl;
}
```