import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    char[] s = S.toCharArray();
    int i = 0;
    int j = s.length-1;
    int ans = 0;
    
    while(i<j){
      if(s[i] != s[j]){
        ans++;
      }
      i++;
      j--;
    }
   
      System.out.println(ans);
    
  }  
}
/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