import java.util.Scanner;
public class Main{
    public static void main(String args[]){
        int cnt=0;
        Scanner sc=new Scanner(System.in);
        String a=sc.next();        
        for(int i=0;i<a.length()/2;i++){
            if(a.charAt(i)!=a.charAt(a.length()-1-i)){
                cnt++;
            }
        }

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