#include <bits/stdc++.h>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define piii pair<int, pii>
#define plll pair<long long, pll>
#define tiii array<int, 3>
#define tiiii array<int, 4>
#define ff first
#define ss second
#define ee ss.ff
#define rr ss.ss
typedef long long ll;
typedef long double ld;
const int INF = (int)1e9 + 7;

using namespace std;

int A[150005][50];
int B[150005][50];

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);

	string S; cin >> S;
	string R(S.rbegin(), S.rend());

	if(S.size() == 1) return !(cout << 1);

	int n = S.size();
	for(int i = 0; i < n; ++i)
	{
		A[i][0] = i + (S[i] == 'b');
		A[i][1] = i + (S[i] == 'a');
		B[i][0] = i + (R[i] == 'b');
		B[i][1] = i + (R[i] == 'a');
		if(A[i][0] == n) A[i][0] = -1;
		if(A[i][1] == n) A[i][1] = -1;
		if(B[i][0] == n) B[i][0] = -1;
		if(B[i][1] == n) B[i][1] = -1;
	}

	int ans = INF;
	int f2 = 1, f1 = 1, f = 2;
	for(int i = 2; i < 50; ++i)
	{
		for(int j = 0; j < n; ++j)
		{
			if(A[j][i - 1] < 0) A[j][i] = A[j][i - 1];
			else if(A[A[j][i - 1]][i - 2] < 0) A[j][i] = A[A[j][i - 1]][i - 2] - f1;
			else A[j][i] = A[A[j][i - 1]][i - 2];
		}
		for(int j = 0; j < n; ++j)
		{
			if(B[j][i - 2] < 0) B[j][i] = B[j][i - 2];
			else if(B[B[j][i - 2]][i - 1] < 0) B[j][i] = B[B[j][i - 2]][i - 1] - f2;
			else B[j][i] = B[B[j][i - 2]][i - 1];
		}
		for(int j = 1; j < n; ++j)
		{
			if(A[j][i - 2] < 0 && B[n - j][i - 1] < 0) ans = min(ans, -A[j][i - 2] - B[n - j][i - 1]);
		}
		f2 = f1, f1 = f, f = f1 + f2;
	}

	cout << ans;
}