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 Java7 (OpenJDK 1.7.0) (judge verdict: Runtime Error)

import java.util.*;
import java.lang.*;
import java.io.*;

public class Main {
    public static void main(String args[]) {
        Scanner scan = new Scanner(System.in);
        
        int x1 = scan.nextInt();
        int y1 = scan.nextInt();
        int x2 = scan.nextInt();
        int y2 = scan.nextInt();
        
        int xdiff = x2 - x1;
        int ydiff = y2 - y1;
        
        if(xdiff >= 0){
            int x3 = x2 - ydiff;
            int y3 = y2 + xdiff;
            int x4 = x3 - xdiff;
            int y4 = y3 - ydiff;
            
            System.out.println(x3+ " "+y3+" "+x4+" "+y4);
        }
        else{
            int x3 = x2 - ydiff;
            int y3 = y2 + xdiff;
            int x4 = x3 - xdiff;
            int y4 = y3 - ydiff;
            
            System.out.println(x3+ " "+y3+" "+x4+" "+y4);
        }
        
    }
}