import java.util.*;

public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    char[] c = sc.next().toCharArray();
    int n = c.length;
    int r = 0;
    for(int i=0;i<n/2;i++){
      if(c[i] != c[n-1-i]){
        r++;
      }
    }
    System.out.println(r);
  }
}
/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