import java.util.*;
import java.io.*;

class Main{
    public static void main(String args[])throws IOException{
      try(BufferedReader br = new BufferedReader(new InputStreamReader(System.in))){
        String[] str = br.readLine().split("");
        
        int i = 0;
        int j = str.length -1;
        int count = 0;

        while(i <= j){
          if(!(str[i].equals(str[j]))){
            count++;
          }
          i++;
          j--;
        }
        System.out.println(count);
      }
    }
}
/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