Rotate Characters in a String

Given a string `s`, return the number of characters that need to be changed to make every substring of length `k` unique. If the substring contains duplicate characters, all duplicates need to be modified to ensure uniqueness within that substring. ### Input Format: - A single line containing the string `s` (1 <= |s| <= 1000). - An integer `k` (1 <= k <= |s|). ### Output Format: - Output a single integer representing the total number of character changes needed. ### Example: Input: abcabc 3 Output: 3 ### Explanation: In the substring 'abc', all characters are unique, but in 'abc' (the second occurrence), 'a' and 'b' repeat and need to be changed.