#include <iostream>
using namespace std;
int main(void) {
	string s;
	cin >> s;
	int cnt = 0, a_cnt = 0;
	for (int i = 0; i < s.size(); ++i) {
		if (s[i] == 'A') {
			cnt += i - a_cnt;
			++a_cnt;
		}
	}
	cout << cnt << endl;
	return 0;
}