# Home

Score : $100$ points

### Problem Statement

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).

### Sample Input 1

3


### Sample Output 1

2


Two pairs can be chosen: $(2,1)$ and $(2,3)$.

### Sample Input 2

6


### Sample Output 2

9


### Sample Input 3

11


### Sample Output 3

30


### Sample Input 4

50


### Sample Output 4

625