import java.util.Scanner;

public class Main {

	public static void main(String[] args) {


		Scanner sc = new Scanner(System.in);
		String[] input = sc.next().split("");
		int hug = 0;
		for(int i = 0; i < (input.length/2);i++) {
			if(!input[i].equals(input[input.length-1 -i])) {
				hug++;
			}
		}
		System.out.println(String.valueOf(hug));

	}

}
/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