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"
)

func main() {
	s := IOInitialize()
	K := Int(s)
	if K%2 == 1 {
		fmt.Println((K/2 + 1) * (K / 2))
	} else {
		fmt.Println((K / 2) * (K / 2))
	}
}

func IOInitialize() *bufio.Scanner {
	s := bufio.NewScanner(os.Stdin)
	s.Split(bufio.ScanWords)
	return s
}

func Int(s *bufio.Scanner) int {
	if !s.Scan() {
		panic("scan error")
	}

	value, err := strconv.Atoi(s.Text())
	if err != nil {
		panic("text to int error")
	}
	return value
}

func String(s *bufio.Scanner) string {
	if !s.Scan() {
		panic("scan error")
	}

	return s.Text()
}

func scanNums(s *bufio.Scanner, len int) (nums []int) {
	for i := 0; i < len; i++ {
		num := Int(s)
		nums = append(nums, num)
	}
	return
}

func scanstrings(s *bufio.Scanner, len int) (strs []string) {
	for i := 0; i < len; i++ {
		str := String(s)
		strs = append(strs, str)
	}
	return
}