import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		String bun;
		do {
		bun = stdIn.next();
		}while(bun.length()<1||bun.length()>100);
		int length = bun.length();
		int count = 0;
		int n;
		if(length %2==0) {
			n = length/2;
		}else {
			n = (length-1)/2;
		}
		for(int i=1 ; i<=n ; i++ ) {
			if(!(bun.substring(i-1,i).equals(bun.substring(length-i,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