#include<stdio.h>
int main(){
	int K, GS,KS;
	scanf("%d",&K);
	GS = K / 2;
	KS = K - GS;
	printf("%d\n",KS*GS);
	return 0;
}
### Prompt

Create a solution in CPP for 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<stdio.h>
int main(){
	int K, GS,KS;
	scanf("%d",&K);
	GS = K / 2;
	KS = K - GS;
	printf("%d\n",KS*GS);
	return 0;
}
```