#include <bits/stdc++.h>
#define fi first
#define se second
#define bit(x) (1LL << (x))
#define getbit(x, i) (((x) >> (i)) & 1)
#define ALL(x) (x.begin(), x.end())
using namespace std;

template <typename T1, typename T2> bool maxi(T1 &a, T2 b) {
    if (a < b) {a = b; return true;} return false;
}

template <typename T1, typename T2> bool mini(T1 &a, T2 b) {
    if (a > b) {a = b; return true;} return false;
}

const int N = 2e5 + 5;
const int oo = 1e9;
const long long ooo = 1e18;

int main() {
    string s;
    cin >> s;
    if(s.size() == 1) {
        cout << 0 << endl;
    }
    else if(s.size() & 1) {
        int res = 0;
        for(int i = 0; i < s.size() / 2; ++i) {
            if(s[i] != s[s.size() - i - 1])
                ++res;
        }
        //cout << s[s.size() / 2  - 1] << " " << s[s.size() - s.size() / 2] << endl;
        if(s[s.size() / 2 - 1] != s[s.size() - s.size() / 2]) {
            cout << res << endl;
        }
        else {
            if(res & 1) {
                ++res;
            }
            cout << res << endl;
        }
    }
    else {
        int res = 0;
        for(int i = 0; i < s.size() / 2; ++i) {
            if(s[i] != s[s.size() - i - 1]) {
                ++res;
            }
        }
        if(s[s.size() / 2] != s[s.size() / 2 - 1]) {
            cout << res << endl;
        }
        else {
            if(res & 1)
                ++res;
            cout << res << endl;
        }
    }
}