import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		String a = sc.next();
      	int count=0;
      	StringBuffer sb = new StringBuffer();
        for (int i = 0;i <a.length() ; i++)
        {          
          if (i< a.length()/2)
          {
          	sb.append(a.charAt(i));
          }
          else
          {
            sb.append(a.charAt(a.length()-i-1));
          }
        }
      	String b=sb.toString();
      	for (int j = 0;j <a.length() ; j++)
        {
          if(a.charAt(j)!=b.charAt(j))
          {
            count+=1;
          }
        }
      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