import java.util.*;
public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        int hug = 0;
        if(str.length()%2 == 0){
            for(int i =0; i<str.length()/2;i++){
                if(str.charAt(i)!=str.charAt(str.length()-1-i)){
                    hug ++;
                }
            }
        }else{
            for(int i =0; i<(str.length()-1)/2;i++){
                if(str.charAt(i)!=str.charAt(str.length()-1-i)){
                    hug ++;
                }
            }
        }
        System.out.println(hug);
    }
}
/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