
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a1;
        int num = 0;

        String s = sc.nextLine();
        a1 = s.length();

        for(int i =0; i < a1/2; i++){
            if(s.charAt(i) != s.charAt(a1-i-1)){
                num++;
            }
        }
        System.out.println(num);

            // write your code here
    }

}

/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