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: Accepted)

s = gets.chomp.to_s

l = s.size

if l == 1
  p 0
else

  if l.even?
    s_front = s[0..l/2-1]
    s_back = s[l/2..l].reverse
  else
    s_front = s[0..l/2-1]
    s_back = s[l/2+1..l].reverse
  end

  count = 0
  s_front.split("").each.with_index do |v,i|
    count += 1 if s_front[i] != s_back[i]
  end
  p count
end