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.

Input

Input is given from Standard Input in the following format:
S

Output

Print 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).

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

见题面 Input 部分

见题面 Output 部分