// !!!!!!
// rename to template.cpp instead of main.cpp
#include <bits/stdc++.h>

#define fr first
#define sc second
#define all(a) (a).begin(), (a).end()

using namespace std;

#ifdef ONPC
mt19937 rnd(223);
#else
mt19937 rnd(chrono::high_resolution_clock::now()
                    .time_since_epoch().count());
#endif

#define TIME (clock() * 1.0 / CLOCKS_PER_SEC)
template<typename T, typename U>
ostream& operator << (ostream& o, const pair<T, U>& p) {
    return o << "(" << p.first << ", " << p.second << ")";
}
template<typename T>
ostream& operator << (ostream& o, const vector<T>& v) {
    bool first = true;
    o << "[";
    for (const auto& l : v) {
        if (!first) o << ", ";
        o << l;
        first = false;
    }
    return o << "]";
}
template<typename T>
ostream& operator << (ostream& o, const set<T>& v) {
    bool first = true;
    o << "{";
    for (const auto& l : v) {
        if (!first) o << ", ";
        o << l;
        first = false;
    }
    return o << "}";
}
#ifdef ONPC
#define show(x) cout << "LINE " << __LINE__ << ": " << #x << "=" << x << std::endl;
#else
#define show(x) 42
#endif

using ll = long long;
using ld = double;

const ll INF = 4'000'000'000'000'000'000LL;

string t;

vector<pair<int, ll>> merge_left_to_right(ll lenL, ll lenR, const vector<pair<int, ll>>& fl, vector<pair<int, ll>>& fr) {
    vector<pair<int, ll>> res(t.size());
    for (int i = 0; i < (int)t.size(); i++) {
        auto cl = fl[i];
        if (cl.first == t.size()) {
            res[i] = cl;
            continue;
        }
        auto cr = fr[cl.first];
        cr.second += lenL;
        res[i] = cr;
    }
    return res;
}

vector<pair<int, ll>> merge_right_to_left(ll lenL, ll lenR, const vector<pair<int, ll>>& fl, vector<pair<int, ll>>& fr) {
    vector<pair<int, ll>> res(t.size());
    for (int i = 0; i < (int)t.size(); i++) {
        auto cr = fr[i];
        cr.second += lenL;
        if (cr.first == -1) {
            res[i] = cr;
            continue;
        }
        auto cl = fl[cr.first];
        res[i] = cl;
    }
    return res;
}

void solve() {
    cin >> t;
    if (t.size() == 1) {
        cout << 1 << "\n";
        return;
    }

    ll len_m2 = 1;
    vector<pair<int, ll>> ltr_m2(t.size());
    vector<pair<int, ll>> rtl_m2(t.size());
    for (int i = 0; i < (int)t.size(); i++) {
        if (t[i] == 'b') {
            ltr_m2[i] = make_pair(i + 1, 1);
            rtl_m2[i] = make_pair(i - 1, -1);
        } else {
            ltr_m2[i] = make_pair(i, 1);
            rtl_m2[i] = make_pair(i, -1);
        }
    }

    ll len_m1 = 1;
    vector<pair<int, ll>> ltr_m1(t.size());
    vector<pair<int, ll>> rtl_m1(t.size());
    for (int i = 0; i < (int)t.size(); i++) {
        if (t[i] == 'a') {
            ltr_m1[i] = make_pair(i + 1, 1);
            rtl_m1[i] = make_pair(i - 1, -1);
        } else {
            ltr_m1[i] = make_pair(i, 1);
            rtl_m1[i] = make_pair(i, -1);
        }
    }

    ll ans = INF;

    while (len_m1 + len_m2 <= INF) {
        for (int i = 0; i < (int)t.size() - 1; i++) {
            if (rtl_m1[i].first == -1 && ltr_m2[i + 1].first == t.size()) {
                ans = min(ans, len_m1 - rtl_m1[i].second - 1 + ltr_m2[i + 1].second);
            }
        }
        ll len_new = len_m1 + len_m2;
        auto ltr_new = merge_left_to_right(len_m1, len_m2, ltr_m1, ltr_m2);
        auto rtl_new = merge_right_to_left(len_m1, len_m2, rtl_m1, rtl_m2);
        len_m2 = len_m1;
        ltr_m2 = ltr_m1;
        rtl_m2 = rtl_m1;
        len_m1 = len_new;
        ltr_m1 = ltr_new;
        rtl_m1 = rtl_new;
        if (ltr_m1[0].first == t.size()) {
            ans = min(ans, ltr_m1[0].second);
        }
        if (rtl_m1[(int)t.size() - 1].first == -1) {
            ans = min(ans, len_m1 - rtl_m1[(int)t.size() - 1].second - 1);
        }
    }

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

int main() {
#ifdef ONPC
    freopen("input", "r", stdin);
#endif
    ios::sync_with_stdio(0); cin.tie(0);
    cout << fixed << setprecision(20);

    int t = 1;
    //cin >> t;
    while (t--) {
        solve();
    }

    cerr << "\n\nConsumed " << TIME << endl;
}