import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
      
      //入力
      String s = sc.next();
      int length = s.length();
      char[] kaibun = s.toCharArray();
      int hug = 0;
      
      //回文になっていない文字を探す
      for(int i = 0; i <length/2; i++){
            if(kaibun[i]!=kaibun[length-1-i]){
            hug++;
            }
      }
       //ハグの最小回数を出力
      System.out.print(hug);
    }
}
   
/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