Problem:
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

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;


public class A{
	
	public static void Main(){
	
		string[] args = Console.ReadLine().Split(' ');
		int k = Int32.Parse(args[0]);
		if( k % 2 == 1 ){
			Console.WriteLine( (k*k - 1)/4 );
		}else{
			Console.WriteLine( k*k/4 );
		}	
		
	}
	
}