import java.util.*;
class Main{
	public static void main(String args[]){
    	Scanner sc = new Scanner(System.in);
      	String s = sc.nextLine();
      	int count = 0;
      	int i = 0, j = s.length() - 1;
      	while( i < j){
          if(s.charAt(i) != s.charAt(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