#include <cstdio>

int main()
{
  int n;
  scanf("%d", &n);
  printf("%d\n", (n / 2) * ((n + 1) / 2));
  return 0;
}
### Prompt

Please formulate a CPP solution to 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 <cstdio>

int main()
{
  int n;
  scanf("%d", &n);
  printf("%d\n", (n / 2) * ((n + 1) / 2));
  return 0;
}
```