import java.util.*;

class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    int cou = 0;
    for(int i = 0; i < s.length()/2; i++){
      if(s.charAt(i) == (s.charAt(s.length()-i-1))){

      }else{
        cou++;
      }
    }
    System.out.print(cou);
  }
}

/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