#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;
    bool ans[s.size() / 2];
    memset(ans, 0, sizeof(ans));
    for(int i = 0; i < s.size() / 2; ++i) {
        if(s[i] != s[s.size() - i - 1]) {
            ans[i] = 1;
        }
    }
    reverse(ans, ans + s.size() / 2);
    // 0 -> wrong
    // 1 -> correct
    int dp[s.size() / 2][2];
    memset(dp, -1, sizeof(dp));
    if(ans[0]) {
        // wrong
        dp[0][1] = 1;
        dp[0][0] = 0;
    }
    else {
        // corect
        dp[0][1] = 0;
        dp[0][0] = 1;
    }
    for(int i = 1; i < s.size() / 2; ++i) {
        // toggle prev wrong
        dp[i][0] = dp[i - 1][0] + 1;
        if(ans[i])
            dp[i][1] = dp[i - 1][0] + 1;
        else
            dp[i][1] = 1e9;
        // not toggle prev correct
        if(ans[i]) {
            // current wrong
            dp[i][0] = min(dp[i][0], dp[i - 1][1]);
            dp[i][1] = min(dp[i][1], dp[i - 1][1] + 2);
        }
        else {
            dp[i][1] = min(dp[i][1], dp[i - 1][1]);
            dp[i][0] = min(dp[i][0], dp[i - 1][1] + 2);
        }
    }
    cout << dp[s.size() / 2 - 1][1] << endl;
}