
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		String s = scan.next();

		int l = s.length();

		int cnt = 0;
		for(int i = 0; i < l/2-0.5; i++) {
			if(s.charAt(i) != s.charAt(l-i-1)) {
				cnt++;
			}
		}

		System.out.println(cnt);


	}
}

/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