import java.util.*;

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        StringBuilder s1 = new StringBuilder(s.substring(0,s.length()/2));
        s1.reverse();
        StringBuilder s2;
        if (s.length()%2==0)s2=new StringBuilder(s.substring(s.length()/2));
        else s2 = new StringBuilder(s.substring(s.length()/2+1));
        int ans = 0;
        for (int i=0;i<s1.length();i++)if (s1.charAt(i)!=s2.charAt(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