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: Wrong Answer)

using System;
using System.Linq;
public class Program{
    public static void Main(){
//        string[] input = Console.ReadLine().Split(' ');
//        int a = int.Parse(input[0]);
//        int b = int.Parse(input[1]);
        int x = int.Parse(Console.ReadLine());
        if(x%2==0){
            Console.WriteLine(x*x/4);
        }else{
            Console.WriteLine(((x/2)+1)*x/2);
        }
    }
}