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 Go (1.6) (judge verdict: Accepted)

package main

import (
    "bufio"
    "fmt"
    "os"
    "strconv"
)

var sc = bufio.NewScanner(os.Stdin)

func read() string {
    sc.Scan()
    return sc.Text()
}

func main() {
	sc.Split(bufio.ScanWords)
	n, _ := strconv.Atoi(read())
	odd := n / 2
	even := (n + 1) / 2
	fmt.Println(odd * even)
}