import java.util.*;
public class Main {
    public static void main(String[] args) {
        long ans = 0;
        Scanner scan = new Scanner(System.in);
        String str = scan.nextLine();
        int l = str.length();
        for (int i = 0; i < l / 2; i++) {
            String a = str.substring(i, i + 1);
            String b = str.substring(l - i - 1, l - i);
            if(!(a.equals(b))) ans++;
        }
        System.out.println(ans);
    }
}
/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