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

p 0 and exit if S.length == 1

s1 = ''
s2 = ''
if S.length.even?
  s1 = S[0..(S.length/2)-1]
  s2 = S[(S.length/2)..-1].reverse
else
  s1 = S[0..(S.length/2)-1]
  s2 = S[(S.length/2)+1..-1].reverse
end

cnt = 0
s1.length.times do |i|
  cnt += 1 if s1[i] != s2[i]
end

p cnt