

import java.util.Scanner;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        StringBuffer sb = new StringBuffer(s.substring((s.length() + 1) / 2));
        String r = sb.reverse().toString();
        int cnt = 0;
        for (int i = 0; i < r.length(); i++) {
            if (r.charAt(i) != s.charAt(i)) {
                cnt++;
            }
        }

        System.out.println(cnt);
        sc.close();
    }
}
/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