import java.util.Scanner;

public class Main {
    //Palindrome-philia
    //改变最少的字符来使得字符串变成回文
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        System.out.println(helper(s));
        sc.close();
    }

    static int helper(String s) {
        int lo = 0, hi = s.length() - 1;
        int count = 0;
        while (lo < hi) {
            if (s.charAt(lo) != s.charAt(hi)) count++;
            lo++;
            hi--;
        }
        return count;
    }
}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz