#include <bits/stdc++.h>
#define pb emplace_back
#define fst first
#define scd second
#define mkp make_pair
#define mems(a, x) memset((a), (x), sizeof(a))

using namespace std;
typedef long long ll;
typedef double db;
typedef unsigned long long ull;
typedef long double ldb;
typedef pair<ll, ll> pii;

const int maxn = 150100;

int n, f[35], g[35][maxn];
char s[maxn];
string t[35];
vector<int> vc[35];

void solve() {
	scanf("%s", s + 1);
	n = strlen(s + 1);
	f[0] = f[1] = 1;
	t[0] = "b";
	vc[0].pb(0);
	t[1] = "a";
	vc[1].pb(1);
	for (int i = 2; i <= 32; ++i) {
		f[i] = f[i - 1] + f[i - 2];
		t[i] = t[i - 1] + t[i - 2];
		vc[i] = vc[i - 1];
		for (int j : vc[i - 2]) {
			vc[i].pb(j);
		}
		vc[i][0] = i;
	}
	for (int i = 1; i <= n; ++i) {
		g[0][i] = (s[i] == 'b');
		g[1][i] = (s[i] == 'a');
	}
	for (int j = 2; j <= 32; ++j) {
		for (int i = 1; i <= n; ++i) {
			g[j][i] = g[j - 1][i] + g[j - 2][i + g[j - 1][i]];
		}
	}
	int ans = 1e9;
	for (int i = 0; i < (int)t[32].size(); ++i) {
		int j = i, k = 1;
		while (j < (int)t[32].size() && k <= n) {
			int p = vc[32][j];
			if (k + g[p][k] > n) {
				if (t[32][j] == 'b') {
					ans = min(ans, j + 1 - i);
					break;
				}
				while (1) {
					int t = -1;
					for (int l = p - 1; l; --l) {
						if (k + g[l][k] <= n) {
							t = l;
							j += f[l];
							k += g[l][k];
							break;
						}
					}
					if (t == -1) {
						ans = min(ans, j + 1 - i);
						break;
					}
					p = t;
				}
				break;
			}
			k += g[p][k];
			j += f[p];
		}
	}
	printf("%d\n", ans);
}

int main() {
	int T = 1;
	// scanf("%d", &T);
	while (T--) {
		solve();
	}
	return 0;
}