#include <bits/stdc++.h>

using namespace std;

int main()
{
	long long a = 0, b = 1;
	string	  s;
	cin >> s;
	long long	ans = (int)size(s);
	deque<char> S(begin(s), end(s)), T;
	for (;;)
	{
		tie(a, b) = pair{b, a + b};
		if (S.size() == 1)
			break;
		if (S.front() == 'b')
			S.push_front('a');
		if (S.back() == 'a')
			S.pop_back();
		if (S.size() == 1)
			break;

		T.clear();
		for (int i = 0; i < (int)size(S);)
		{
			if (S[i] == 'a')
			{
				if (i < (int)size(S) - 1 && S[i + 1] == 'b')
				{
					T.push_back('a');
					i += 2;
				}
				else
				{
					T.push_back('b');
					i++;
				}
			}
			else
			{
				T.push_back('a');
				i++;
				ans += b;
			}
		}
		S.swap(T);
	}
	cout << ans;
}