import java.util.Scanner;
import java.lang.String;

public class Main {

    public static void main(String[] args) {
        int A1;
        int num = 0;
        Scanner scan = new Scanner(System.in);
        String S = scan.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);
    }
}
/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