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 Ruby (2.7.1) (judge verdict: Wrong Answer)

#標準入力を取得し、1文字ずつの配列としてinput_s1に格納
input_s1 = gets.split("")

#標準入力の文字数を取得
input_cnt = input_s1.size

#標準出力用変数を初期化
output_cnt = 0

#配列のi番目と文字数-iを比較
(1..input_cnt/2).each do |i|
  if input_s1[i-1] == input_s1[input_cnt-i]
  else
    output_cnt += 1
  end
end

#回答を出力
puts output_cnt