// File generated on 24/11/13 20:14 by Anand

#include <bits/stdc++.h>
using namespace std;

#define fastio ios::sync_with_stdio(false); cin.tie(0)
#define rep(i, m, n)  for (long long i = m; i < n; i++)
#define DEBUG(x) cout << "debug: " << x << "\n"
#define YES cout << "YES\n"
#define NO cout << "NO\n"
#define pb push_back
#define sz size

typedef long long ll;
typedef pair<ll,ll> pll;
typedef vector<ll> vec;
typedef vector<vec> vecc;
typedef vector<pll> vecp;

void SOLVE() {
    string s;
    cin >> s;
    ll n = s.size();
    ll m = ceil(n/2.0);
    vec a(m);
    ll ans = 0;
    rep(i,0,m) 
        if (s[i] == s[n-1-i]) a[i] = 1;
    vec x;
    ll c = 0, p = a[0];
    rep(i,0,m) {
        if (a[i] == p) c++;
        else {p = a[i]; x.pb(c); c = 1;}
    }
    if (c > 0) x.pb(c);
    ll st = 0;
    if (a[0] == 1) st = 1;
    //rep(i,0,x.size()) cout << x[i] << " ";
    //cout << "\n";
    for(ll i = st; i < x.size();) {
        if (x[i]%2==0) ans += x[i]/2;
        else if (i+2 < x.size() && x[i+1] <= 2 && x[i+2]%2 == 1) {ans += ((x[i] + x[i+2]) / 2 + 2); i+=2;}
        else if (x[i] == 1 && i < x.size() - 1 && n%2 == 0) ans += 2;
        else if (x[i] == 1 && i < x.size() - 2 && n%2 == 1) ans++;
        else if (x[i] == 1) ans++;
        else ans += (x[i] - 1) / 2 + 1;
        i+=2;
    }

    cout << ans << "\n";
}

signed main() {
    fastio;

    //ll _;
    //cin >> _;

    //while(_--) 
		SOLVE();

    return 0;
}