Minimum Operations to Palindrome

You are given a string s consisting of lowercase English letters. Your task is to determine the minimum number of operations required to transform the string into a palindrome. In one operation, you can change one character of the string to any other character. Note that you only need to change one end of a mismatched pair (i.e. for indices i and n-i-1 if s[i] != s[n-i-1]) to make the string a palindrome.

Formally, let n be the length of the string. Considering all indices 0 ≤ i < n/2, if s[i] != s[n-i-1] then an operation is required. Therefore, the answer is the number of such mismatched pairs.

Examples:

• For s = "abc", the answer is 1.
• For s = "aabb", the answer is 2.
• For s = "racecar", the answer is 0.

inputFormat

The input consists of a single line containing the string s (which may be empty) composed of lowercase English letters.

Input Format:

s

outputFormat

Output a single integer representing the minimum number of operations required to transform the string into a palindrome.

Output Format:

answer

## sample

abc

1