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 Pascal (FPC 2.6.2) (judge verdict: Accepted)

uses
  SysUtils,
  Classes;
  
 procedure MainProc;
	var
		input, oddNum : Integer;
	begin
	ReadLn(input);
	oddNum := (input div 2) + (input mod 2);
	WriteLn(oddNum * (input - oddNum));
	end;
  
begin
MainProc;
end.