#include<iostream>
#include<algorithm>
#include <vector>
#include<cmath>
#include<iomanip>
#include<queue>
using namespace std;
typedef long long int lint;
int main() {
	string S;
	cin >> S;
	int Z = S.size();
	int cnt = 0;
	int sum = 0;
	for (int ia = 0; ia < Z; ia++) {
		if (S.at(ia) == 'A') {
			sum += ia - cnt;
			cnt++;
		}
	}
	cout << sum << endl;
}