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
#include<stdio.h>
int main(void)
{
  int k,gu,ki;
  scanf("%d",&k);
  gu=k/2;
  ki=k-gu;
  printf("%d",gu*ki);
  return 0;
}