import java.util.*;
import java.math.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int cnt = 0;
        char ch[] = new char[s.length()];
        int r = s.length();
        for (int i = 0; i < r; i++) {
            ch[i] = s.charAt(i);
        }
        for (int i = 0; i < r / 2; i++) {
            if (ch[i] != (ch[r - 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