#include<bits/stdc++.h>
#define rep1(i, a, b) for(int i = a; i <= b; ++i)
#define rep2(i, a, b) for(int i = a; i >= b; --i)
#define ll long long
#define ft first
#define sd second
#define pb push_back
#define pii pair <int, int> 
#define ptc putchar
#define ld long double
#define debug puts("-------------------")
const int N = 2e5 + 10, k = 30;
using namespace std;
int n, f[N][35], v[35], pos; string s;
int query(int ql, int qr, int l = 1, int r = v[k], int p = k) {
   // if(qr - ql + 1 == 9) cout << pos << ' ' << ql << ' ' << qr << ' ' << l << ' ' << r << ' ' << p << '\n';
   if(l >= ql && r <= qr) return pos + f[pos][p];
   int mid = l + v[p - 1] - 1;
   // if(qr - ql + 1 == 5) system("pause");
   if(ql <= mid && pos <= n) pos = query(ql, qr, l, mid, p - 1);
   if(qr > mid && pos <= n) pos = query(ql, qr, mid + 1, r, p - 2);
   return pos;
}
bool chk(int l, int r) {
   pos = 1;
   return query(l, r) > n;
}
int main() {
   cin >> s; n = s.size(); s = " " + s;
   rep1(i, 1, n) f[i][s[i] == 'a'] = 1;
   v[0] = v[1] = 1;
   rep1(i, 2, k) v[i] = v[i - 1] + v[i - 2];
   rep1(j, 2, k) rep1(i, 1, n) {
      f[i][j] = f[i][j - 1];
      int nxt = i + f[i][j - 1];
      if(nxt > n) continue;
      f[i][j] += f[nxt][j - 2];
   }
   // cout << f[1][0] << ' ' << f[1][1] << ' ' << f[2][0] << ' ' << f[2][1] << ' ' << f[1][2] << '\n';
   // return 0;
   int r = 1, ans = 1e9;
   rep1(l, 1, v[k]) {
      if(r < l) r = l; while(r <= v[k] && !chk(l, r)) ++r;
      if(chk(l, r)) ans = min(ans, r - l + 1);
      // if(chk(l, r) && r - l + 1 == 9) return cout << l << ' ' << r << '\n', 0;
   } cout << ans << '\n';
   return 0;
}