#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using vl = vector<ll>;
#define sz(c) ll((c).size())
#define FOR(i, a, b) for(ll i=(a);i<(b);i++)

#define all(c) begin(c),end(c)
#define pb push_back
#define FORD(i, a, b) for(ll i=(b)-1;i>=(a);i--)
using vvl = vector<vl>;
using pll = pair<ll, ll>;
using vpll = vector<pll>;
#define xx first
#define yy second
#define TR(X) ({if(1) cerr << "TR: " << (#X) << " = " << (X) << endl;})
const ll oo = 0x3f3f3f3f3f3f3f3f;

ll conv(ll a1, ll a2, ll b1, ll b2) {
    if (a1 != b1 && a2 != b2)
        return 1;
    if (a1 == b1 && a2 == b2)
        return 0;
    return 2;
}

ll convArr[27][27][27][27];

int main() {
    cin.sync_with_stdio(0);
    cin.tie(0);
    ll n;
    string a;
    cin >> a;
    n = sz(a);
    vl s;
    for (char &c: a) s.pb(c - 'a');

    vector<vvl> dp(n / 2, vvl(26, vl(26, 1e9)));
    dp[0][s[0]][s.back()] = 0;

    FOR(c1, 0, 27)FOR(c2, 0, 27)FOR(c3, 0, 27)FOR(c4, 0, 27) convArr[c1][c2][c3][c4] = conv(c1, c2, c3, c4);

    FOR(i, 1, n / 2) {
        FOR(c1, 0, 26)
            FOR(c2, 0, 26)
                FOR(c3, 0, 26)
                    FOR(c4, 0, 26) {
                        ll val = oo;
                        for (ll x: vl{c1, c2, 26}) {
                            val = min(val, dp[i - 1][c1][c2] + convArr[c1][s[i]][x][c3] + convArr[c2] [s[n - i - 1]][x][c4]);
                        }
                        dp[i][c3][c4] = min(dp[i][c3][c4], val);
                    }
    }
    ll ans = oo;

    FOR(c1, 0, 26) FOR(c2, 0, 26) {
            ans = min(ans, dp[n / 2 - 1][c1][c2] + (c1 != c2));
            if (ans == 0) {
                TR(c1);
                TR(c2);
            }
        }

    cout << ans << endl;
}