    import java.util.*;
	import java.lang.Math;
    public class Main {
    	public static void main(String[] args) {
    		Scanner scan = new Scanner(System.in);
			String original="";
			original=scan.nextLine();
			int count=0;
			int len=original.length();
			for(int i=0;i<len/2;i++)
			{
				if(original.charAt(i)==original.charAt(len-1-i))
				{}
				else
					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