Problem:
Score : 200 points

Problem Statement

Takahashi loves palindromes. Non-palindromic strings are unacceptable to him. Each time he hugs a string, he can change one of its characters to any character of his choice.

Given is a string S. Find the minimum number of hugs needed to make S palindromic.

Constraints

S is a string consisting of lowercase English letters.

The length of S is between 1 and 100 (inclusive).

Input

Input is given from Standard Input in the following format:

S

Output

Print the minimum number of hugs needed to make S palindromic.

Sample Input 1

redcoder

Sample Output 1

1

For example, we can change the fourth character to o and get a palindrome redooder.

Sample Input 2

vvvvvv

Sample Output 2

0

We might need no hugs at all.

Sample Input 3

abcdabc

Sample Output 3

2

Solution in Go (1.6) (judge verdict: Accepted)

package main

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

var (
	read  = bufio.NewReader(os.Stdin)
	write = bufio.NewWriter(os.Stdout)
)

func yesno(result bool) {
	if result {
		fmt.Fprintln(write, "Yes")
	} else {
		fmt.Fprintln(write, "No")
	}
}

func main() {
	defer write.Flush()

	var s string
	fmt.Fscan(read, &s)

	cnt := 0
	n := len(s)
	for i := range s {
		if s[i] != s[n-1-i] {
			cnt++
		}
	}
	fmt.Fprintln(write, cnt/2)
}