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 (2.3.3) (judge verdict: Wrong Answer)

s = gets.chomp.to_s
w_length = s.length
f_half = nil
l_half = nil
count = 0

if w_length.even?
  f_half = s.slice(0, w_length / 2).split('')
  l_half = s.slice(w_length / 2, w_length / 2).split('')
  f_half.each_index do |idx|
    count += 1 if f_half[idx] != l_half.reverse[idx]
  end
else
  s.slice!(w_length / 2 + 1)
  f_half = s.slice(0, w_length / 2).split('')
  l_half = s.slice(w_length / 2 + 1, w_length / 2).split('')
  f_half.each_index do |idx|
    count += 1 if f_half[idx] != l_half.reverse[idx]
  end
end
puts count