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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var swr = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(swr);
            int ans = 0;
            StringBuilder s = new StringBuilder();
            s.Append(Console.ReadLine());
            int count = 0;
            string temp = string.Empty;
            for (int i = 0; i < s.Length / 2; i++)
            {
                // Console.WriteLine("Compare " + s[i] + " : " + s[(s.Length - 1) - i]);
                if (s[i] != s[(s.Length - 1) - i])
                {
                    s[i] = s[(s.Length - 1) - i];
                    count++;
                }
            }
            Console.WriteLine(count);

            Console.Out.Flush();
        }
    }
}