import java.util.*;
import java.io.*;
 
public class Main {
    public static void main (final String[] args) {
        final Scanner sc = new Scanner(System.in);
        String str = sc.next();
      	int count = 0;
      	for (int i = 0; i < str.length()/2; i++) {
          if (str.charAt(i) != str.charAt(str.length() - i - 1)) 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