/* -*- coding: utf-8 -*-
 *
 * 3774.cc:  No.3774 Minimum Cost For Palindrome - yukicoder
 */

#include<cstdio>
#include<cstring>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 1000000;

/* typedef */

/* global variables */

char s[MAX_N + 4];

/* subroutines */

/* main */

int main() {
  scanf("%s", s);
  int n = strlen(s);

  int cnt = 0;
  for (int i = 0, j = n - 1; i < j; i++, j--)
    if (s[i] != s[j]) cnt++;

  printf("%d\n", cnt);
  
  return 0;
}