import java.util.*;
public class Main
{
  public static void main(String[] args)
  {
    Scanner input = new Scanner(System.in);
    String s = input.next();
    
    int i=0,j=s.length()-1;
    int g = 0;
    while(i<j)
    {
      if(s.charAt(i)!=s.charAt(j))
        	g++;
      i++;
      j--;
    }
    
    System.out.println(g);
   }
}

/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