#include <iostream>
#include <string>

int main() {
	std::string s;
	std::cin >> s; std::cin.ignore();

	int count=0;
	for (int i = 0; i < s.size(); ){
		if (s[i]=='B' && s[i+1]=='A') {
			auto t = s[i];
			s[i] = s[i+1];
			s[i+1] = t;
			count++;
			i = 0;
		}
		else {
			i++;
		}
	}
	std::cout << count << std::endl;
	return 0;
}