import java.util.Scanner;
class Main{
	public static void main(String[] aegs){
    	Scanner sc = new Scanner(System.in);
      	String s = sc.next();
      	int count = 0;
      	int i =	0;
      	int j = s.length() - 1;
      	for(;i<j;){
        	if(s.charAt(i) != s.charAt(j))
            	count++;
            i++;
            j--;
        }
        System.out.println(count);
      	sc.close();
    }
}
/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