#include <iostream>
#include <string>

using namespace std;

int main() {
	string s;
	cin >> s;

	int ans = 0;
	while (!s.empty()) {
		if (s.back() == 'B') {
			s.pop_back();
			continue;
		}

		int pos = s.find_last_of('B');
		if (pos == string::npos) {
			break;
		}
		swap(s[pos], s[pos + 1]);
		ans++;
	}

	cout << ans << endl;
	return 0;
}