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# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Text;

namespace B
{
    class Program
    {
        static void Main(string[] args)
        {
            string S = Console.ReadLine();
            StringBuilder SB = new StringBuilder(S);
            int n = SB.Length;
            n--;
            int cnt = 0;
            for(int i=0;i<n;i++)
            {
                if (i * 2 <= n)
                {
                    if (SB[i] != SB[n - i])
                    {
                        cnt++;
                    }
                }
            }
            Console.WriteLine(cnt);
        }
    }
}