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: Accepted)

S = gets.strip.to_s
M = S.size
cnt = 0
if M%2==0 then
  (0..M/2-1).each do |i|
    if S[i]!=S[M-1-i] then
      cnt += 1
    end
  end
  puts cnt
else
  (0..(M-3)/2).each do |i|
    if S[i]!=S[M-1-i] then
      cnt += 1
    end
  end
  puts cnt
end