import java.util.Scanner;
public class Main{
    public static void main(String[] args){
	Scanner scanner = new Scanner(System.in);
	String s = scanner.nextLine();
	int count = 0;
	for(int i = 0;i < s.length() / 2;i++){
	    if(!(s.charAt(i) == s.charAt(s.length() - i - 1))){
		count++;
	    }		
	}
	System.out.println(count);
    }
}

/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