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.Diagnostics;
using System.Linq;

namespace PaizaTest
{
    class Program
    {
        static void Main(string[] args)
        {
            var str = Console.ReadLine();
            var centerIndex = str.Length / 2;
            // 6 / 2 = 3
            // 012345
            // abcabc
            // 7 / 2 = 3
            // 0123456
            // abcdcba
            var diffCount = 0;
            for (int i = 0; i < centerIndex; i++)
            {
                if (str[i] != str[str.Length - 1 - i])
                {
                    diffCount++;
                }
            }
            Console.WriteLine(diffCount);

        }
    }
}