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: Accepted)

import java.util.*;

public class Main {
  
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int K = sc.nextInt();
    
    int ans = 0;
    for (int i = 1; i <= K-1; i++) {
      boolean even = i % 2 == 0;
      for (int j = i + 1; j <= K; j++) {
        if (even && j % 2 == 1 || !even && j % 2 == 0) {
            ans++;
        }
      }
    }
    
    System.out.println(ans);
  }
}