#include<bits/stdc++.h>
#define L(i, j, k) for(int i = (j); i <= (k); ++i)
#define R(i, j, k) for(int i = (j); i >= (k); --i)
#define ll long long
#define sz(a) ((int) (a).size())
#define vi vector < int >
#define me(a, x) memset(a, x, sizeof(a))
#define ull unsigned long long
#define ld __float128
#define pb emplace_back
using namespace std;
#define i128 __int128
using namespace std; 
const int N = 2e6 + 7, D = 30;
string S[35];
vi L[35];
string tt;
int n;
char t[N];
int mt[N][35];
int main() {
	ios :: sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	S[0] = 'b', L[0] = vi{0};
	S[1] = 'a', L[1] = vi{1};
	L(i, 2, D) {
		S[i] = S[i - 1] + S[i - 2];
		for(auto&u : L[i - 1])
			L[i].pb(u);
		for(auto&u : L[i - 2])
			L[i].pb(u);
		L[i][0] = i;
	}
	// L(i, 1, 150000)tt += 'b';
	cin >> tt;
	n = sz(tt);
	L(i, 1, n) {
		t[i] = tt[i - 1];
	}
	L(i, 0, D)mt[n + 1][i] = n + 1;
	R(i, n, 1) {
		L(j, 0, D)mt[i][j] = i;
		if(t[i] == 'b') mt[i][0] = i + 1;
		if(t[i] == 'a') mt[i][1] = i + 1;
		L(j, 2, D) {
			mt[i][j] = mt[mt[i][j - 1]][j - 2];
		}
	}
	int ans = 1e9;
	L(pp, 0, sz(S[D]) - 1) {
		int pos = pp, cur = 1;
		while(pos < sz(S[D]) && cur <= n) {
		int p = L[D][pos];
		if(p) {
		R(j, p, 1) {
			if(j == 1 || mt[cur][j] <= n) {
				cur = mt[cur][j];
				pos += sz(S[j]);
				break;
			} 
		}
		}else {
			if(t[cur] == 'b') {
				++cur;
			}
			++pos;
		}
		}
		if(pos != sz(S[D])) {
			ans = min(ans, pos - pp);
		}
	}
	cout << ans << '\n';
	return 0;
}