#include <bits/stdc++.h>
using namespace std;
int main(){
  int k;
  cin>>k;
  cout<<((k+1)/2)*(k-(k+1)/2);
}
### Prompt

In CPP, your task is to solve the following problem:

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+1)/2)*(k-(k+1)/2);
}
```