#include<bits/stdc++.h>
using namespace std;
int main ()
{
    int cnt = 0, n;
    char s[102];
    scanf("%s", s);
    n = strlen(s);
    n /= 2;
    int l = strlen(s)-1;
    for (int i = 0; i<n; i++) {
        if (s[i] != s[l-i]) cnt++;
    }
    printf("%d\n", cnt);
    return 0;

}
