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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.Scanner;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
	int a = sc.nextInt();
    if (a%2==1){
      System.out.println(((a/2)+1)*(a/2));
    } else {
      System.out.println(((a/2)+1)*((a/2)+1));
    }
  }
}