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)

# 入力
s = gets.chomp

# 文字列を半分にする
b = s.size/2
moji = s.insert(b,",")
c = moji.split(",")

#2つを比べやすくする
mae = c[0]
ushiro = c[1]
ushiro =ushiro.reverse
d = [mae,ushiro]
e = d.all?{mae==ushiro}

# こたえ
if e == false
  puts b-mae.count(ushiro)
else
  puts 0
end