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)

require 'pp'

def gets; ARGF.gets; end

class Solver

  def initialize
  end

  def main
    s = gets.chomp

    h_len = s.length / 2
    if h_len == 0
      puts 0
      return
    end

    ans = 0
    0.upto(h_len-1) do |i|
      if s[i] != s[s.length-i-1]
        ans += 1
      end
    end

    puts ans
  end
end

if __FILE__ == $0
  Solver.new.main
end