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 Common Lisp (SBCL 1.1.14) (judge verdict: Accepted)

;; B - Palindrome-philia

(defun solve (S)
  (let ((len (length S)))
    (loop for i from 0 below (ash len -1)
      count (not (equal (char S i) (char S (- (1- len) i)))))))

(let ((S (read-line)))
  (princ (solve S))
  (fresh-line))