import java.io.IOException;
import java.util.Scanner;

class Main {
    private static final Scanner scanner = new Scanner(System.in);
    public static void main(final String[] args) throws IOException {
            String s = scanner.nextLine();
            int ans = 0;
            for (int i = 0; i < (s.length()/2); i++) {
                if (!s.substring(i, i + 1).equals(s.substring(s.length()-i -1, s.length()-i))) {
                    ans++;
                }
            }
            System.out.println(ans);
        }
}

/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