import java.util.*;
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    String s = sc.next();
    
    int sHalfLength = s.length() / 2;
    String sFront = "";
    String sBack = "";
    int count = 0;
    
    if (s.length() % 2 == 0) {
      sFront = s.substring(0, sHalfLength);
      sBack = s.substring(sHalfLength, s.length());
      for (int i = 0; i < sHalfLength; i++) {
        if (sFront.substring(i, i+1).equals(sBack.substring(sHalfLength - i - 1, sHalfLength - i))) {
        } else {
          count++;
        }
      }
    } else {
      sFront = s.substring(0, sHalfLength);
      sBack = s.substring(sHalfLength + 1);
      for (int i = 0; i < sHalfLength; i++) {
        if (sFront.substring(i, i+1).equals(sBack.substring(sHalfLength - i - 1, sHalfLength - i))) {
        } else {
          count++;
        }
      }
    }
    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