import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);

        String s = sc.next();
        char[] arr = s.toCharArray();
        int n = s.length();


        int cnt = 0;
        if (n%2==0 || n%2==1){
            for (int i=0; i<n/2; i++){
                if (arr[i]!=arr[n-i-1]){
                    cnt++;
                }
            }
            System.out.println(cnt);
        }else {
        }

    }

}
/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