import java.util.Scanner;

class Main{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String[] str = s.split("");
		int count = 0;
		for(int i=0;i<str.length;i++){
			if(!(str[i].equals(str[str.length -1 - i]))){
				str[str.length - 1 - i] = str[i]; 
				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